Interview with Backend Engineers from Mercari, Merpay, Mercoin, and Souzoh: “The Kind of Person that Fits Our Company!”

Currently, Mercari, Merpay, Mercoin, and Souzoh are looking for Backend Engineers.

In an effort to highlight the features and appeal of each of these companies, we interviewed Carlos Donderis (@CaDs) of Mercari, Godric Cao (@godriccao) of Merpay, Sadaaki Hirai (@sadah) of Mercoin, and Keigo Watanabe (@keigow) of Souzoh and talked to them about the kinds of engineers they would like to work with.

As a company group, we share the same core values, but interestingly, when we asked our interviewees about how their companies differed from each other, we began to see some variety in the kind of person who would fit in at each company.

Featured in this article

  • Carlos Donderis(@CaDs)

    Mercari, Director of Engineering. Carlos has a degree in Computer Science from Universidad Complutense de Madrid. He worked as a Software Engineer across Europe, Latin America, and for the past ten years, in Japan where he first worked for the GMO Group and later Sansan. He joined Mercari as an Engineering Manager in 2019, mainly focused on the Product teams.

  • Godric Cao(@godriccao)

    Merpay Manager of Managers. Godric joined Mercari in November 2017. Prior to this, he was in charge of developing a global loyalty platform at Rakuten, launching a cross-border e-commerce business at Wyingo, and developing a travelog service at Wanderlust.

  • Sadaaki Hirai(@sadah)

    Mercoin Backend Engineer. After graduating from university, Sadaaki joined a system integrator company as a new graduate. He then joined, where he was involved in developing an online reservation service for restaurants. In January 2015, he joined Goodpatch and was appointed CTO in December 2015. Nearly three years later, in November 2018, he joined Mercari. After serving as Engineering Manager of the entire Mobile team, he was also put in charge of hiring engineers in the Engineering Office team. He is currently a Software Engineer for Mercoin.

  • Keigo Watanabe(@keigow)

    Software Engineer/Engineering Manager at Souzoh. Keigo joined DeNA in 2010 where he was in charge of Backend/iOS development for social games and new businesses. In 2016, he joined the first Souzoh where he worked on developing Mercari “Atte.” He became a Product Manager in 2018 at the same time as the launch of Merpay. After working as an Engineering Manager for the Backend team and as a Manager of Engineering Managers, he moved to the new Souzoh in April 2021. Currently, he is mainly in charge of organizational development and recruitment.

Let’s take a look at the features of each company.

Expanding or launching services: What is the development structure for each phase of your company?

ーWould you please tell us about the services you provide, their phases, and their development structure?

@CaDs: Mercari is one of the largest CtoC marketplaces in Japan. Therefore, the scale of our engineering department is comparatively larger than those at Merpay, Mercoin, and Souzoh, and our backend, client, and web departments are collectively becoming a large development organization, but we’re still not big enough.

Our engineering organization is divided into the Product Division, responsible for application maintenance and feature development, and the Foundation Division, responsible for developing core services commonly used within the product division. Lastly, the Infrastructure Division provisions the infra and ensures that all systems continue to operate without any problems.

@CaDs: People often make the mistake of thinking that “Mercari is finished, and that there is nothing else to do”. This is not the case. There are still a lot of things to do, improvements to make, and new things to work on.

ーWhat about Merpay and Mercoin?

@godriccao: The company I work for, Merpay, provides the mobile payment service that the company takes its name from, and which exceeded 10.67 million users in June 2021. On a scale of 0-100, Merpay’s service phase is in the 10 to 100 stage. The pillars of our business are already set, but we are now working on future growth, profitability, and new challenges.

And just so you know, Merpay’s team structure is a matrix.

Team structure of Merpay

@godriccao: The vertical axis of this graph shows the teams organized by product. The members of the teams represented on the vertical axis are the people who usually work together. Each team has Product Managers (PM), Backend Engineers, Client Engineers, and so on. Next, the horizontal axis shows the reporting line. So for example, the manager of a Backend engineer is the Engineering Manager (EM) shown by the respective vertical line. Although, some of the EMs manage multiple teams.

@sadah: At Mercoin, which is where I work, we are just starting up, and we’re in the 0-1 phase. We plan to work in cryptoassets and NFTs(non-fungible tokens) and to design and develop our product.

We still don’t have a lot of people, but we are gradually building a team structure. We have several software engineers and PMs working on cryptoassets and NFTs, respectively. Each team is divided according to the technical area they are in charge of (back-end or client-side). Each member has a microservice that they are in charge of designing and developing.

ー And what about at Souzoh, @keigow?

@keigow: Souzoh was established in January 2021, and at the end of July 2021, we pre-launched a service called “Mercari Shops”. It’s been about two months since we had the official release. So the service has been released, but it feels like we are in the 0 to 1 phase.

Team structure of Souzoh

@keigow: Our team structure is pretty simple:. There are two product development teams whose development work is supported by the Enabling Team*. A team consists of about ten people, including several software engineers. The engineers don’t have specific job assignments, but some tend to be better at working on the back-end while others are better on the front-end.

* Souzoh’s Enabling Team is a team whose mission is to increase the productivity of the product teams. It is made up of SRE(Site Reliability Engineer), machine learning engineers and front-end specialists.

What kind of challenges and growth can professionals expect to gain as Mercari Group engineers?

ー What kind of challenges do you think engineers who join Mercari, Merpay, Mercoin or Souzoh will have the chance to take on, and what kind of growth do you think they will achieve in five years?

@CaDss: Every month, 20 million users use Mercari, so we must always be aware of the scale of our service. Engineers who join our company are faced with the challenge of ensuring and improving performance and scalability and providing a good user experience (UX). And the mission of the Mercari Group is “create value in a global marketplace (where anyone can buy & sell)”. So although we are providing our services in Japan, we also have the challenge of expanding overseas.

Through the development experience that our members gain at Mercari, they’ll be able to grow into engineers who can solve a variety of problems and develop services for millions of people. There is a concept of “all software engineers” at Mercari. After joining the company as a Back-end engineer, members can select various career steps, including client development, web, machine learning, and management. It’s left up to the individual to decide whether they want to become specialists in one field or generalists.

Photo from left to right: @CaDs (Mercari), @godriccao (Merpay)

@godriccao: There are two main challenges at Merpay. The first is that Merpay is the payment and ID infrastructure for the entire Mercari Group. We need to ensure that it supports payments linked to new businesses such as Souzoh’s Mercari Shops as well as Mercoin. It’s an interesting and difficult challenge.

Secondly, Merpay itself is in the FinTech domain and demands financial-level engineering. We developed an AI credit model, and we also built a financial system that can guarantee transactions for the massive volume of traffic coming from Mercari, Merpay, Souzoh and other group companies. Providing the best UX possible, rather than just achieving functionally, is also a big challenge.

Not limited to Merpay, for the entire Mercari Group, there are three career paths: Engineering Specialist, Tech Lead (TL), and EM.

Merpay also has a rotation program. This allows our members to grow within Merpay or rotate to another group company. When a new service is launched, they can join it as well. The possibilities are endless.

ーWhat about Mercoin and Souzoh?

@sadah: At Mercoin, we plan to follow the same technology stack as the rest of the Mercari Group. However, we want to use our experience building microservice architectures at Merpay and other companies to create an even better foundation at Mercoin. We can now come together to examine design system parts such as these. This will be a big challenge for us technically.

The areas of cryptoassets and NFTs that Mercoin handles are being commercialized by R4D (R&D organization at Mercari) following internal verification testing and validation. These are new areas of technology for us, but there we do have a certain degree of base knowledge. I think it would also be interesting to launch a business together with members who have been engaged in research at R4D.

Mercoin’s mission is “circulate your value, anywhere and everywhere.”. While Mercari is a marketplace where goods and legal tender (Japanese yen) change hands, Mercoin deals with digital data and rights that are not physical objects, such as cryptoassets and NFTs. We are just getting started, but there are many areas we want to take on.

When I imagine what it would be like to be one of our engineers five years from now, I picture someone who has been able to develop their expertise in the areas of cryptoassets and NFTs. They would also be able to develop their expertise in a specific technology area, such as Go or GCP. Incidentally, I joined Mercoin through a rotation program. Five years from now, once we’ve created other new services, our people will likely be able to find challenges there.

@keigow: Souzoh uses the APIs of Mercari and Merpay, but the e-commerce part is developed from scratch and loosely coupled. This allows us to easily adopt new technologies when necessary. For example, we use GraphQL, Monorepo, Cloud Run, and other optimal technologies as needed. The organization is not large, so we have an environment where it’s easy to take on the challenge of new technologies.

I believe that through their experience as engineers at Souzoh, our members will be able to expand their depth and breadth in terms of technology. What’s more, they’ll also be able to acquire problem-solving skills.

As mentioned earlier, all of the engineers at Souzoh are software engineers, and we don’t create boundaries such as frontend or backend. We already have about 30-40 microservices, but we don’t assign a person to each microservice. Instead, everyone is involved with what they need, when they need it. In this sense, we have an environment where it’s easy for our members to get deeply involved in one technology and broaden their scope as engineers, such as backend engineers involved in the frontend.

The other thing is that people want to be as actively involved as possible when they’re hungry for a challenge. Since members’ roles are fluid rather than set in stone, they can fix both the frontend and backend by themselves and then do the release. As a result of this, our members should be able to become engineers who can solve problems independently.

Enthusiastic about solving social issues with technology, loves a challenge… What kind of person best fits each company?

ーWhat kind of person do you think would be a good fit for your company?

@CaDs: Many of the remaining challenges at Mercari are technically complex. We are looking for people who can solve or are interested in complex issues. We are also looking for people good at time management and problem-solving skills. This is because they need to understand the technology used at Mercari, the issue of bottlenecks, and how to make a service scalable. They need to proceed with development from all manner of perspectives.

The next thing is that Mercari has a large development team and group companies that work with us. We require our engineers to have good communication skills. We communicate with each team and cooperate with them right up until the final release. Therefore, it’s important to have the attitude of finding solutions together, not just sticking to your part of the project. In addition, things change quickly at Mercari, so it’s important to have a flexible and open mind.

Lastly, Mercari would like to expand into various markets outside of Japan in the future. We are looking for candidates in Japan and worldwide because we want to incorporate diverse perspectives to achieve better service development. We are also promoting D&I (Diversity & Inclusion), so we are looking for people who are accepting and who will recognize people’s diversity.

@godriccao: At Merpay, we are looking for people who share our mission – “Building trust for a seamless society.” Another thing we are looking for is a candidate who has a good understanding of the complex and challenging FinTech domain and who has the enthusiasm and confidence to solve social issues with technology.

From left to right: @sadah (Mercoin), @keigow (Souzoh)

@sadah: At Mercoin, I think you will fit in easily if you can enjoy the challenge of launching a new financial service. There are various stakeholders inside and outside the company, so coordination is key. We also have to consider security for product design. As a result, there are times when we cannot proceed with development at our own pace. However, Mercoin wants to overcome these challenges and significantly impact society. There is a lot of work involved in launching a financial service, but I hope people who enjoy a challenge will join us.

Also, if you have experience in finance or cryptoasset development, your skills will make you a good fit. However, even if you don’t have such experience, if you have been working on cryptoassets or NFTs individually and want to take on a new challenge, we want to work with you.

Currently, we are launching products and also launching an organization at the same time. So, I think this is a suitable environment for people interested in developing products and setting up an organization.

@keigow: Since Souzoh has just started, it’s suitable for people who enjoy the challenges of working at a start-up.

And at Souzoh, in addition to the Mercari Group’s values of “Go Bold,” “All for One,” and “Be a Pro,” we have “Move Fast” as our motto. Mercari Shops has a lot of potential and should grow to an even bigger scale. However, we are still in the start-up phase, so there remains a lot of uncertainty.

I want to work with people who have a sense of speed and are willing to try new initiatives straight away—people who, even if they fail, can enjoy making the improvements needed to do better.

What each company looks for in the hiring process

ーCould you describe your hiring processes and selection points?

@CaDs: First, we give the candidate a technical assignment. After they pass, they will proceed to a technical interview with an engineer. Later, they will interview with an Engineering Manager and finally, there is an interview with the Director or VP, which mainly focuses on the culture and whether or not they can grow within Mercari.

We look at their experience with programming languages and building solutions. Our primary languages are Go and PHP, so familiarity with these languages is preferred, but experience with other compiler languages is also fine. Also, since Mercari is built on a very complex distributed system, experience in developing distributed systems is important. We also check their architectural design skills.

On the non-technical side, we look to see if the candidate fits into our brand of engineering and culture. It’s essential to know whether they fit with the values and mission of Mercari. We also ask questions related to conflict resolution within the team, such as handling disagreements and managing projects. In other words, it’s important to have both technical skills and soft skills.

@godriccao: The key points for interviews at Merpay are empathy for the business, culture fit, and technical ability and potential.

The first is, as I mentioned earlier when talking about the type of person who would be a good fit, is whether they share the mission of Merpay and want to work with us. The second point, culture fit, is the same across the entire Mercari Group: a commitment to the Group’s values of Go Bold, All for One, and Be a Pro. Finally, we look for technical ability and potential.

Since Merpay is a FinTech business, a single failure can become a significant, irreversible problem that we cannot undo. We check whether the candidate can do the right kind of engineering in such a rugged business area. We use Go for development, but experience with this programming language is not a must. We place importance on a person’s experience in developing large-scale systems, their basic knowledge of CS and software engineering, and their potential.

ーWhat about at Mercoin and Souzoh?

@sadah: At Mercoin, we do an initial document screening. After that, there are technical assignments, for which the candidate can choose to use either Go or Java. After that, there are two to three interviews. The order of the selection process may vary slightly.

As for technical issues, the candidate will be asked to implement something according to the specifications we provide. Our engineers will then review their code. The duration of the assignment is one week, but we can adjust this to accommodate family circumstances and how busy they are. When I transferred to Mercoin, I also took on the challenge of these technical assignments. I worked on them on weeknights and weekends while still doing my regular job, and it was quite a challenge. It was interesting because the challenge tested my knowledge of backend development. So I hope people will give these challenges a try to test their abilities. Also, in the interview, we ask if they relate to our business and our mission.

@keigow: One of the unique things about Souzoh is that we conduct a system design interview. It’s to see if they can write code and if they have the problem-solving skills that are important when working at a start-up. The interview lasts 40 to 60 minutes, and the interviewer and the candidate discuss how to approach the challenges that engineers at Souzoh face.

For example, we ask them how they would create an architecture with good performance when creating a specific function. There is no one correct answer to this, and there are trade-offs between doing one thing and not doing another. What we are looking at is their approach. The system design interview is a part of the standard selection process for software engineers, but the assignment we discuss with them is prepared so that they can show us what areas they are good at.

And just so you know, we ask candidates about whether they share our mission and values during the interview with the EM and CTO.If you would like to see Souzoh’s detailed selection guide(written in Japanese), it’s available on GitHub, so if you’re interested in working with us, please be sure to take a look.

To wrap things up, pitch your company to our readers!

ーIs there anything you would like to say in closing?

@CaDs: Mercari is one of the largest CtoC marketplaces in Japan. We face massive challenges daily and test the latest technologies in our services to provide value to millions of customers. Come and help us find innovative ways to improve our systems and achieve a superior UX together.And finally, join us in the global expansion of Mercari!

@godriccao: As the payment infrastructure that supports the entire Mercari Group, Merpay has the challenge of continuously scaling up its technology to match the growth speed of the whole group. In addition, we have an environment where FinTech innovations can occur. If you share Merpay’s mission and want to grow with the company, we are looking forward to hearing from you!

@sadah: Launching a new financial service for such things as cryptoassets and NFTs is tough, but we want to enjoy this challenge together. We are looking forward to working with people who share Mercoin’s mission of “circulate your value, anywhere and everywhere.”!

@keigow: As a new business, we are in the 0-1 start-up phase, and the engineering and organization are in a good position to take on various challenges. We are looking forward to working with you to Move Fast for our business’s success!

ーThank you for sharing your time today!

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