Backend Engineer

Job Description PayPay is looking for a Backend Engineer to work on our payment system to deliver the best payment experience for our customers. AI-First Culture at PayPay At PayPay, we believe that the future of software development is AI-augmented. Every engineer is expected to actively leverage AI tools for code reviews, testing, documentation, debugging, and productivity. AI is not optional — it is a mandatory part of our daily engineering workflow. Candidates must demonstrate both experience and mindset in utilizing AI effectively to deliver high-quality systems faster and better. Main 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. Tech Stack We select the best combination of tech at times. | Java, Kotlin, Scala | Spring Boot, JUnit, Reselience4j, Feign | MySQL/AuoraDB, DynamoDB, ELK, Kafka, Redis, TiDB | Docker, Kubernetes, ArgoCD, AWS, GCP | GitHub, IntelliJ, Gradle, Maven, npm/yarn, Flyway, Jenkins, snyk, | Bigquery, Kibana, Spark | PlantUML, draw.io, miro.com | Slack, Zoom Qualifications 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. Preferred Qualifications 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.