Senior Android Developer

About KOMOJU

KOMOJU is the leading cross-border payment gateway for Japan. We power payments for companies like video game distribution platform Steam and the popular mobile app TikTok. Today we help thousands of merchants by providing them with the payment infrastructure they need through developer-friendly API’s to integrations on popular platforms like Shopify and Wix; we help our merchants grow in all markets they are expanding.

What to expect

We are product focused, meaning you will work on our payment gateway and any other projects towards building the future of KOMOJU. You will work with other engineers in a flat and inclusive culture where engineers have a say in both key product and technology decisions. The culture is largely self-organizing, which means engineers have both a stake and ownership in what they work on. Engineers play to their strengths, but are also able to invest in areas where they want to grow within the team. At KOMOJU, you are the main driver behind your growth and position in the company.

International at our core

Most of our engineering team members come from outside Japan. English is the primary language used, and throughout the company, many people are at least bilingual.

Being an international company we know the importance of bilingualism. We offer all employees a choice between optional English and Japanese lessons to help create a culture of diversity and ensure smooth collaboration across teams.

About the Position

We are looking for our first Senior Android Developer to help build KOMOJU’s Point of Sale (POS) application and native mobile apps, which implements our Platform API for payment processing. As our first Android engineer, you will play a key role in defining coding standards, architectural decisions, and the frameworks we adopt.

Our ideal candidate has strong experience building mobile applications and is eager to expand across languages and frameworks to deliver exceptional mobile experiences. Testing and code quality are central to our engineering culture, so a solid understanding of testing principles and methodologies is essential.

We are not just looking for a standard mobile developer, but for a Systems-on-Android Engineer. You should have expert-level proficiency in Kotlin and Java, with the ability to write high-performance, thread-safe, and maintainable code.

This position sits at the intersection of application logic and hardware integration. You will be responsible for integrating SDKs that control IC card readers, NFC modules, magstripe readers, and PIN pads. Success in this role requires experience with low-level hardware event handling, Android background service communication (AIDL/IPC), and complex state machine management.

Knowledge of the EMV protocol and payment transaction flows is a plus. However, as EMV processing is specialized, we prioritize engineers with strong architectural discipline who can design robust, testable systems and quickly master hardware documentation.

Responsibilities

• Develop KOMOJU POS, native merchant apps and mobile SDK offerings using Kotlin.
• Collaborate with product managers and other developers to define, design, and ship new features.
• Work across tech stacks with backend engineers to design and implement features for mobile applications.
• Flexibility to engage with other programming languages and work on our platform backend as needed.
• Technical design and architecture review across both mobile platforms (iOS and Android).

Requirements

Who you are

• Minimum 5+ years of experience.
• Experience with Android SDK and mobile development lifecycle.
• Familiarity with RESTful APIs to connect mobile applications to back-end services.
• Strong knowledge of mobile UI/UX principles, patterns, and best practices.
• Generalist (T-shaped developer), able to jump between multiple areas of our tech stack to get the job done.
• Ability to work effectively in a collaborative team environment.
• Knowledge of cross-platform frameworks for iOS and Android is welcomed.

Nice to Have

These aren't required, but be sure to mention them in your application if you have them.

• Some experience of iOS development and general familiarity with iOS architecture is welcomed.
• Experience working for a Japanese business.
• Lead and coach other members of the team, fostering skill development and high performance.
• Business-level proficiency in Japanese.

What is the process like?

We aim to keep our hiring process thoughtful and efficient, typically involving 3-4 stages depending on the role: an initial screening, a take-home assignment, a technical (team) interview with live coding exercise, and a final interview with leadership. Throughout the process, the team evaluates candidates not only on technical skills but also on their alignment with team culture and potential for long-term growth.

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Benefits

• At KOMOJU, we embrace remote work while also offering office space for those who prefer in-person collaboration
• 10 days regular vacation, additional 5 days summer, and 5 days winter vacation
• Paid birthday holiday
• Budget for self-learning allowance, to ensure our employees’ skills remain current
• Access to the O’Reilly Learning Platform
• Language training for Japanese/ English
• Twice a week office lunch
• Although we are a remote-first company, this role is based in Tokyo, and candidates must be willing to relocate to Japan.