Full Stack Engineer, Tech Lead Track

About KATIX

KATIX is an online auction platform for high-value used goods, built around trust and transparency. Individuals sell. Only registered businesses bid. We started with motorcycles and cars, and we are planning to expand beyond vehicles.

The entire sale happens online. A seller photographs their vehicle and uploads the documents from their phone, the listing goes to auction, and the sale completes without a trip to a shop. That is a different mechanism from traditional buyback, and it puts real weight on engineering: how easy the upload is, and how accurately the vehicle comes across to bidders, decide whether a deal closes.

The company was founded in 2006 (formerly Interfirm, renamed to match the platform) and is about 70 people today, average age around 27, more than 60 percent women. Around 20 new hires join in April 2027. The engineering team works in a mix of Japanese and English.

Our direction is explicit: an AI-native engineering organization measured on business outcomes, not on features shipped. That shapes who we hire and how we interview.

The role

You join as a full stack engineer on a defined path to tech lead. At KATIX a tech lead is someone who knows the product, the business, and the codebase well enough to lead a small team on the strength of good calls, not on title.

This track is for people who already work this way: you take a feature from an ambiguous ask to production on your own, you review other people's code and your feedback changes it, you see blockers before they land, and people around you have started coming to you for direction. You do not need the title yet. You need to already be doing the work.

The split is roughly 75 percent hands-on development and 25 percent leading people: code review as a first-class responsibility, mentoring one or two engineers, unblocking others, and facilitating the team's Kanban rhythm.

We already have strong builders. What we need next is people who can build and also lift the people around them, and who care about what the work does for the business.

What you will work on

• Frontend and backend features across the platform in Next.js (App Router) and TypeScript, with Prisma and PostgreSQL
• Auctions, escrow, the seller upload and verification flow, buyer tooling, and internal dashboards
• The AI pipeline: verification of seller submissions (photos, documents) and price intelligence, built on foundation-model APIs (Claude, Gemini), plus the internal agents that help other departments ship
• AWS (ECS, RDS, S3), Docker, GitHub Actions; CI reliability and testing
• Kanban planning, daily standups, retrospectives

A note on the stack, stated plainly: the car platform is Next.js and TypeScript. The bike platform still carries a Rails and Vue legacy that we are migrating. You will meet both.

The two things that matter most

1. You are serious about KATIX specifically. Not about changing jobs, not about growing as an engineer in general. You have looked at the product, you understand what we are trying to do for people selling a vehicle, and you have a concrete reason to want to do it here. We ask about this in every interview.

2. You use AI to move faster, and you can show it. You work with AI coding agents daily. You know how to break work into pieces an agent can handle, how to verify what comes back, and when not to use it at all. You can point to something concrete that went faster or better because of how you used AI. We look at this directly in the technical interview.

What we are looking for

Required

• 2 to 5 years of professional web engineering, full stack
• You work independently: you own features end to end, from an unclear request through design, build, review, and release
• Your code review is real. You give feedback that changes what ships, and you take feedback the same way
• You spot risks, blockers, and bad assumptions early and say so
• Solid grounding in a modern web framework (React or Next.js preferred), API design, relational databases, and data modeling
• Daily hands-on use of AI coding agents (Claude Code, Cursor, Copilot agent mode, or similar), including decomposing tasks for them and verifying their output
• Some experience mentoring or informally leading: reviewing for others, pairing, onboarding someone
• Clear communication with non-engineers, and genuine interest in the business side of what you build (the metrics your work moves: listing rate, closing rate, lead time to listing)
• Japanese at roughly JLPT N3 level. You can handle day-to-day casual conversation with colleagues outside engineering. Engineering discussions can happen in English.

Nice to have

• Evidence that you have accelerated your own or your team's delivery with AI
• Hands-on Next.js, TypeScript, Prisma, or PostgreSQL
• Rails or Vue
• AWS beyond the basics (ECS, ECR, IAM), Docker in production
• Observability and reliability work (Sentry, New Relic, SLOs)
• Prior experience as a tech lead or team lead
• Marketplace, e-commerce, auction, or escrow-adjacent product experience

Where this goes

Performance reviews are every six months. Tech lead of a Kanban team is the next step, typically within 12 to 18 months for the right person. After that, either the management track (leading a team, then an engineering manager role as the department grows) or the specialist track (architecture, platform, AI infrastructure). You choose.

Benefits

• Transparent compensation table, with performance reviews every six months
• Two performance bonuses per year
• Housing allowance if you live near Shibuya
• Dedicated budget for learning, certifications, and study
• Flextime with core hours from 10:00 to 16:00
• Hybrid work: one to two remote days per week depending on level, after the first six months
• Company-covered team lunches when three or more people go together
• Optional weekly study session; the team attends tech events and conferences together

Selection process

1. Casual interview with the Engineering Manager (about 30 minutes, English is fine)
2. First interview with the Engineering Manager
3. Technical interview
4. Final interview with the CEO.

Typically two to four weeks from casual interview to decision.

Before applying, ask yourself

• Given the right resources, how confident am I that I can build anything I am asked to build?
• Can I describe a time I changed how a team works, and what it did to their output?
• Why do I want to work at KATIX, and would that reason survive if I swapped in any other company's name?

If you can build, and your reason is specific to KATIX, apply. If your reason is "to grow as an engineer," you can do that anywhere, including here, and it is not enough on its own.

How to apply

You do not need a perfect resume. Tell us about a team you led, how it worked, and why KATIX. We would love to hear from you.