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