Senior Backend Engineer - Application Foundation

The Team

The Common Foundation team helps engineering teams move faster by providing scalable, reliable, and reusable systems that serve as the platform for product development. The Application Foundation side focuses on building core backend services and APIs that reduce duplication, clarify ownership, and enable product teams to deliver sophisticated features efficiently.

We design systems that support integration at scale, with an emphasis on abstraction, reliability, and long-term maintainability.

The Role

We're looking for a Senior Backend Engineer who thrives at the intersection of architecture, execution, and business understanding.

In this role, you'll lead the design and evolution of backend systems that serve as shared infrastructure across product teams. You'll help re-architect legacy components pragmatically, shape platform-level tools, and create services that turn complex business needs into flexible technical building blocks.

What You'll Do

• Design and implement scalable backend services and APIs that support cross-team usage and reduce redundancy.
• Translate complex and evolving business requirements into modular systems with clear separation of responsibilities.
• Drive re-architecture efforts that balance delivery speed, reliability, and long-term maintainability.
• Collaborate with product teams to ensure foundation systems empower them to move fast without reinventing the wheel.
• Apply strong testing, observability and monitoring practices to ensure operational excellence.
• Work across service boundaries and repositories to design cohesive solutions.
• Guide system design discussions and mentor team members on architecture, reliability, and code quality.

Tech Stack

We use a modern, cloud-native architecture. You don’t need to be fluent in everything, but familiarity with several is highly valued:

• Languages: Go (primary), TypeScript, Python
• APIs: gRPC, REST, Protocol Buffers
• Infrastructure: AWS (EKS, RDS, S3), Kubernetes, AWS Amplify, RDS Proxy
• CI/CD & GitOps: GitHub Actions, ArgoCD
• Observability: Datadog (APM, metrics, logs)
• Databases: Amazon Aurora (MySQL-compatible), Vector DB, Redis
• Search: OpenSearch
• Realtime Communication: WebSockets, Server-Sent Events (SSE), gRPC streaming
• Authentication & Identity: AWS Cognito, JWT, internal session systems
• Frontend Touchpoint: React (via product teams), OpenAPI/.proto SDK generation

What We're Looking For

Required

• 5+ years of backend software engineering experience, with a track record of delivering robust, scalable systems.
• Proficient in at least one backend programming language and open to working across stacks.
• Deep understanding of API design, data modeling, distributed systems, and software abstraction principles.
• Experience working on systems used by multiple product teams or customer-facing domains.
• Familiarity with service-oriented or micro-service architectures and tooling such as gRPC, Protocol Buffers, Kubernetes, CI/CD platforms, and observability tools like Datadog.
• Ability to collaborate across backend, frontend, and infrastructure disciplines with strong communication skills.

Bonus

• Understanding of the Identity Provider (IDP) domain and security concerns such as authentication flows, token management, and session modeling.
• Experience working with modern AI agent tooling or MCP (Model Context Protocol) server architectures.
• Familiarity with frontend technologies or patterns - enabling better API design and integration.
• Exposure to multi-tenant systems, permission models, or platform product design.
• Contributions to internal developer tooling, libraries, or DX initiatives.

Why Join

• Opportunity to contribute to innovative new product development and build systems from scratch.
• Leadership and career development opportunities.
• Remote-friendly and flexible work schedules.
• Work in a diverse, global team environment.
• Excellent benefits and perks such as Resort Worx, book purchasing, free weekly lunch, offsites, and more.

Working Style

Hybrid Work
We follow a hybrid work style, combining both office and remote work. Recommended in-office days vary by role. Even when working remotely, we maintain smooth collaboration and communication through tools like Zoom, Google Meet, and Gather.

Flex Work
You can customize your working hours to suit your day. For business and client-facing teams, schedules are often arranged around client meetings.

Global Environment
With team members from over 20 countries, we bring together diverse perspectives and ideas, driving projects forward across languages and cultures in an environment where English and Japanese blend naturally into daily communication.

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Position Details

Job Title: Backend Engineer - Application Foundation
Employment Type: Full-time
Salary Range: ¥4,000,000 – ¥10,000,000 per year
The actual offer will be decided based on your experiences and skills.
Location: Tokyo, Japan (Hybrid work style)
Probation Period: 6 months (same conditions during probation)

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