Join one of Japan's largest digital services companies as a Kotlin Backend Engineer, developing and maintaining high-performance Web APIs that support a global platform used by hundreds of millions of users.

You will work on core membership and security services using Kotlin, Java, Vert.x, MariaDB, and Cassandra, building scalable backend components for user profiles, authentication, login alerts, password verification, and other essential platform functionality.

This is an opportunity to strengthen your expertise in backend development, Web API engineering, distributed systems, and large-scale platform architecture while collaborating with an international engineering team in Tokyo.
Key Responsibilities

• Develop, scale, and maintain high-performance membership Web APIs supporting large-scale global platform services.
• Design and implement secure backend components using Kotlin, Vert.x, MariaDB, and Cassandra.
• Build and maintain critical security services, including user profile management, login alerts, and password verification.
• Collaborate with multicultural engineering teams within an Agile development environment to deliver reliable platform functionality.
• Monitor, troubleshoot, and optimise backend system performance using OpenCensus and the ELK Stack.
• Identify performance bottlenecks and technical issues while improving the scalability, stability, and reliability of backend services.

Required Skills and Qualifications Experience:

• Professional software development experience using Kotlin and Java, with a strong focus on Web API development.
• Experience designing and developing scalable APIs using asynchronous frameworks such as Vert.x.
• Hands-on experience working with relational databases such as MariaDB and NoSQL databases such as Cassandra.
• Strong understanding of backend application development, API design, system performance, and scalable architecture.
• Experience developing reliable backend services within production web application environments.

Soft Skills:

• Strong analytical and problem-solving skills with a detail-oriented engineering mindset.
• Collaborative approach and the ability to work effectively within an Agile engineering team.
• Ability to communicate technical ideas clearly and work effectively with multicultural and cross-functional teams.
• Proactive approach to troubleshooting, performance optimisation, and continuous improvement.

Language Requirements:

• English: Business level or above for effective communication in a global technology environment.
• Japanese: Basic level.

Preferred Skills & Qualifications

• Experience working with cloud infrastructure, particularly Google Cloud Platform (GCP).
• Familiarity with Docker and Kubernetes for containerisation and orchestration.
• Experience or knowledge of microservices architecture.
• Exposure to CI/CD pipelines and automated deployment processes.
• Experience developing high-concurrency or large-scale backend platforms.
• Familiarity with monitoring and observability technologies such as OpenCensus and the ELK Stack.

About the Company
Our client operates one of Japan's largest digital service ecosystems, reaching hundreds of millions of users globally across e-commerce, fintech, digital media, and other online services.

As part of the company's central platform engineering environment, developers work on high-concurrency, large-scale backend infrastructure that supports critical membership and user services.

The organisation provides an international and technology-driven environment where engineers can collaborate with experienced global talent while developing their expertise in Kotlin, backend engineering, Web APIs, cloud technology, and scalable distributed systems.
Why You'll Love Working Here

• Develop large-scale backend APIs supporting a global digital platform used by hundreds of millions of users.
• Strengthen your technical expertise across Kotlin, Java, Vert.x, MariaDB, Cassandra, and distributed backend systems.
• Gain exposure to modern technologies including GCP, Docker, Kubernetes, microservices, and CI/CD.
• Work alongside multicultural and international engineering teams in a global technology environment.
• Enjoy a flexible hybrid work model.
• Access an on-site employee food hall with complimentary meals.
• Work comfortably in a modern, casual dress environment.

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