Senior Full stack Engineer

Job Description As a Senior Full stack Engineer, you will drive system design and development across both frontend and backend architectures. Working closely with Product, Design, and AI Infrastructure teams, you will establish engineering standards, mentor developers, and deliver scalable engagement solutions for enterprise clients in Japan and globally. Key Responsibilities Architecture & Development: Lead the design and implementation of scalable frontend and backend systems, customer-facing applications, and internal tools. System Design: Architect robust APIs, backend services, and platform integrations while leading technical decisions and trade-off discussions. Product Collaboration: Partner with Product and Design teams to shape user experiences and long-term product direction. Quality & Operations: Drive continuous improvements in system reliability, scalability, performance, and observability. Engineering Standards: Establish modern engineering practices, write maintainable tested code, and refine development workflows. Mentorship & Leadership: Guide and mentor engineers through code reviews, technical guidance, and collaborative problem-solving. Troubleshooting: Diagnose and resolve complex production incidents within distributed systems. End-to-End Ownership: Take full ownership from requirements definition through to production deployment and operations. Requirements Must-Have Skills: Experience: 5+ years of professional software engineering experience in Agile/Scrum environments. Language Proficiency: Business-level fluency or higher in English for cross-functional collaboration. Fullstack Development: Strong experience in modern web development using frontend frameworks (e.g., React, Vue, Next.js) and backend technologies (e.g., Node.js, Python, Elixir, Ruby, PHP). Backend & API Design: Proven experience designing scalable APIs, backend services, and relational databases (PostgreSQL or MySQL). System Architecture: Deep understanding of software architecture, system design, and technical trade-offs. Production & Leadership: Hands-on experience with production operations and leading technical projects or mentoring developers. Preferred Skills: Experience with statically typed languages (TypeScript, Python type hints) or functional programming (Elixir/Phoenix). Knowledge of gRPC, Protocol Buffers, event-driven architecture, and distributed systems. Familiarity with conversational AI, LLM-based application development, or AI-assisted development tools. Experience building scalable SaaS platforms or working in high-growth startups. Benefits Location: Choice of Tokyo or Osaka office. Work Style: Hybrid work environment (1 day per week in the office). Hours: Flextime (core hours 10:00–16:00) or discretionary labor system depending on grade. Benefits: Full social insurance, commuter allowance, device provision, and up to ¥55,000 for books and training seminars. Leave: Weekend/national holidays, paid leave, summer/year-end holidays, and Life & Health support leave.