Full-Stack Engineer (Backend Focus)

Full-Stack Engineer (Backend Focus) Company Description Rokken is a software development company that provides customized technical solutions for clients. Our work combines machine learning, real-time 3D visualization, medical software, and AI-powered web applications. Website: https://rokken.tech/ Main office: S-Cube108, 130-42 Nagasonecho, Kita Ward, Sakai, Osaka 591-8025, Japan Job Offer Description We are looking for a Full-Stack Engineer with a backend focus to help build and integrate the web systems behind our AI and software products. This role sits between backend development, web application development, service integration, and AI product workflows. You will help design APIs, connect frontend features to backend services, integrate AI/ML components into product systems, and make our applications easier to develop, operate, and extend. We are a small engineering team, so this is a high-ownership role. We need someone who can understand a product end to end, make practical technical decisions, and work closely with frontend, backend, platform, and machine learning engineers. Annual Compensation 6,000,000 to 9,500,000 yen Language Requirements English: Business level required Japanese: Not required, but nice to have Minimum Experience Mid-level or above. This is an ownership-heavy role, but we are not necessarily looking for a senior specialist. We care more about solid engineering fundamentals, good judgment, clear communication, and the ability to learn and take responsibility for systems over time. In This Role, You Will Build backend services, APIs, and product workflows for AI and software products. Integrate frontend features with backend services, databases, workers, and external systems. Help connect AI/ML components into user-facing web applications. Design data models, API contracts, background jobs, and service boundaries. Improve reliability, maintainability, and debuggability of application code. Work with frontend engineers to deliver complete product features. Work with ML engineers to turn research or model outputs into usable product behavior. Collaborate with platform engineers on deployment, observability, and runtime requirements. Write tests, review code, and help maintain a clean development workflow. Document technical decisions, integration behavior, and operational details. Minimum Qualifications 3+ years of professional experience in web application development. Strong backend development experience with Python, TypeScript, Node.js, or a similar stack. Experience designing and maintaining APIs. Experience with relational databases such as PostgreSQL. Practical frontend experience with a modern web framework such as React, Next.js, Vue, or similar. Ability to understand product requirements and translate them into reliable technical implementation. Experience working with Git-based development workflows and code review. Ability to debug issues across frontend, backend, database, and service boundaries. Strong problem-solving, documentation, and communication skills. Preferred Qualifications Experience building or integrating AI/ML-powered product features. Experience with Python backend frameworks such as FastAPI, Django, Flask, or similar. Experience with TypeScript and modern frontend application architecture. Experience with background workers, queues, scheduled jobs, or workflow orchestration. Experience with Temporal.io or similar workflow orchestration systems. Experience with Docker and containerized development environments. Experience with CI/CD and production or production-like deployments. Experience with authentication, authorization, permissions, and secure API design. Experience with observability, logging, and debugging distributed systems. Experience with data-heavy applications, annotation workflows, review tools, or internal productivity tools. Interest in using modern AI agents to improve engineering workflows. Working Style This is not a pure frontend role and not a pure backend-only role. We are looking for someone who enjoys building complete product features, especially where backend services, frontend UX, data flows, and AI/ML systems need to work together. You do not need to be an expert in every tool listed above. We care more about strong fundamentals, good judgment, clear communication, and the ability to own systems over time. We are an AI-forward engineering team, and we especially value people who already use modern AI agents in their daily development work. Support For Foreign Candidates Assistance with visa renewal or visa application. Help with finding housing. Support for daily life in Japan, such as city office registration and opening a bank account. Trial Period 3 months. Remote Work Policy Regular collaboration with our Osaka/Sakai-based team is important for this role, especially during onboarding and early product delivery. Initial phase: on-site work preferred. After initial assessment: flexible work arrangements may be possible, depending on project needs and collaboration requirements.