Backend Engineer

**About the company:** PayPay Minato-ku, Tokyo With over 70M million registered users (as of July 2025), PayPay is the country’s most popular mobile wallet used by approximately one out of every two smartphone users in Japan. **Responsibilities:** Design large-scale systems with high complexity to support our high throughput applications. Understand how to leverage infrastructure for solving such large-scale problems. Develop tools and contribute to open source wherever possible. Adopt problem solving as a way of life – always go to root cause! Support the code you write in production. Leverage AI/LLM-based tools for code development, reviews, testing, and documentation in daily workflows. Requirements 4+ years of experience in using Java under professional environment, or if you are non-Java user, excellent skills in generalized programming languages, such as Scala, Python, and Go. Interest and ability to learn other coding languages as needed. Experience with NoSQL databases and distributed cache. Strong fundamentals in data structures, algorithms and object-oriented programming. In-depth understanding of concurrency and distributed computing. Degree in Computer Engineering or Computer Science or 5+ years equivalent experience in SaaS platform development. Business level of English or Japanese. Hands-on experience with AI/LLM tools (e.g., ChatGPT, GitHub Copilot, Gemini, CodeWhisperer, or similar) in professional software development. Nice to haves While not specifically required, tell us if you have any of the following. Experience with implementing platform components such as RESTful APIs, Pub/Sub Systems, Database clients. Experience with AWS services. Experience in working for system development in finance, payment, or similar industries. Experience in system design, development of web systems which handle massive amount of transactions or require scalability. Language ability in Japanese and English is a plus (we have a professional translator but it is nice to have language skills). Experience in microservices. Proven track record of integrating AI-assisted development into system design and delivery. Contributions to AI-related open-source projects or automation of workflows with AI is a plus. APPLY FOR THIS POSITION DO YOU NEED MORE INFO? ASK A QUESTION Meet PayPay's Developers Growing your career by asking for you want with Ashwini Meshram Ashwini leads one of PayPay’s payment sub-teams. She got there by doing something she’s done throughout her career: identifying something she wants to do and asking to do it. Read their story... Refactoring PayPay’s Android App with Adrian Mariadas Adrian came to Japan to join PayPay as an Android Engineer. As the app has grown in scope, refactoring the codebase to ensure development can continue at a rapid pace has been a big part of his job. Read their story... iOS Development at PayPay with Yoseph Savianto Yoseph joined PayPay after being attracted to their mission of making Japan a cashless society. As an iOS Engineer, he originally joined their iOS feature team, but now works on their platform team, creating an internal SDK for their iOS and Android apps. Read their story... Rapidly scaling to tens of millions of users with Shilei Long Shilei started working on PayPay before it launched, and has seen it grow into a product used by tens of millions of users. He explains how diversity has helped them overcome challenges, and what PayPay is looking for in candidates. Read their story... **Requirements:** 4+ years of experience in using Java under professional environment, or if you are non-Java user, excellent skills in generalized programming languages, such as Scala, Python, and Go. Interest and ability to learn other coding languages as needed. Experience with NoSQL databases and distributed cache. Strong fundamentals in data structures, algorithms and object-oriented programming. In-depth understanding of concurrency and distributed computing. Degree in Computer Engineering or Computer Science or 5+ years equivalent experience in SaaS platform development. Business level of English or Japanese. Hands-on experience with AI/LLM tools (e.g., ChatGPT, GitHub Copilot, Gemini, CodeWhisperer, or similar) in professional software development. **Nice to have:** While not specifically required, tell us if you have any of the following. Experience with implementing platform components such as RESTful APIs, Pub/Sub Systems, Database clients. Experience with AWS services. Experience in working for system development in finance, payment, or similar industries. Experience in system design, development of web systems which handle massive amount of transactions or require scalability. Language ability in Japanese and English is a plus (we have a professional translator but it is nice to have language skills). Experience in microservices. Proven track record of integrating AI-assisted development into system design and delivery. Contributions to AI-related open-source projects or automation of workflows with AI is a plus. APPLY FOR THIS POSITION DO YOU NEED MORE INFO? ASK A QUESTION Meet PayPay's Developers Growing your career by asking for you want with Ashwini Meshram Ashwini leads one of PayPay’s payment sub-teams. She got there by doing something she’s done throughout her career: identifying something she wants to do and asking to do it. Read their story... Refactoring PayPay’s Android App with Adrian Mariadas Adrian came to Japan to join PayPay as an Android Engineer. As the app has grown in scope, refactoring the codebase to ensure development can continue at a rapid pace has been a big part of his job. Read their story... iOS Development at PayPay with Yoseph Savianto Yoseph joined PayPay after being attracted to their mission of making Japan a cashless society. As an iOS Engineer, he originally joined their iOS feature team, but now works on their platform team, creating an internal SDK for their iOS and Android apps. Read their story... Rapidly scaling to tens of millions of users with Shilei Long Shilei started working on PayPay before it launched, and has seen it grow into a product used by tens of millions of users. He explains how diversity has helped them overcome challenges, and what PayPay is looking for in candidates. Read their story...