Fullstack Lead Engineer (Tokyo)

Mico provides Mico Engage AI, a high-traffic enterprise SaaS used daily by major companies, and we are currently hiring core members to join our team. In our fast-growing startup environment, you will have the opportunity to directly shape the product and elevate the user experience. You will be expected to proactively tackle a wide range of challenges—including optimizing high-traffic systems, designing and developing new AI-powered features, and improving our real-time processing infrastructure. Working closely with our Lead Engineer, you will drive product-critical development while also contributing to technical decision-making and standardization. By collaborating in a multicultural, bilingual team, you will sharpen your skills in a global development environment. This role offers far more than pure development—you will play a key part in the growth of both the team and the product, making it a highly rewarding position. What You Will Gain Experience building scalable systems and implementing AI technologies Collaboration skills in a global engineering team Hands-on experience driving product growth end-to-end Tech Stack Web Backend: TypeScript (NestJS), Go, Elixir Web Frontend: TypeScript (Next.js), Chakra UI Databases: TiDB, Aurora MySQL, DynamoDB, MemoryDB for Redis Infrastructure: AWS (Cognito, EC2, ECS, Route53, Lambda, Kinesis, SQS, SES, RDS, API Gateway), IaC (Terraform, AWS CDK) Monitoring & Analytics: New Relic, Sentry, CloudWatch, BigQuery, Metabase CI/CD & Tools: Docker, GitHub Actions, Amplify, Slack, Notion, Jira Responsibilities Stabilizing the Mico Engage AI delivery infrastructure: Build and improve the infrastructure that enables stable, large-scale delivery even for clients with high user volumes. Developing new features: Implement product-enhancing features based on our product roadmap. Customer-driven development: Build high-impact, reusable features based on needs identified through Customer Success activities. Requirements 5+ years of hands-on experience in system development Experience developing with TypeScript and React Full-stack engineering experience (both frontend and backend) Ability to independently handle the full development cycle from requirements definition to release 2+ years of code review experience Ability to write test code and contribute to improving product quality Experience in technical decision-making (evaluating technical requirements, cost, and maintainability) 2+ years of experience leading development as a technical lead (teams of 5+ members) Experience designing REST APIs Business-level proficiency in Japanese Nice to haves Experience developing with Go or Next.js Experience designing systems using Domain-Driven Design or Clean Architecture Experience developing gRPC APIs Ability to effectively leverage AI to improve development speed and quality Experience in infrastructure setup (AWS, Docker, etc.) Business-level proficiency in English Hiring process steps Document Screening + Coding Test Casual Interview (Japanese Language Check) First Interview Second Interview Third Interview Final Interview + Reference Checks Job Offer Meeting