Build Payment Systems That Power Japan's E-Commerce Revolution

Ever wondered what it's like to write code that processes millions of real transactions? To see your work directly impact how people shop across Japan's biggest platforms? This is your chance.

We're building the payment infrastructure that's reshaping Japanese fintech—and we need engineers who get excited about
Scala, functional programming, and solving complex distributed systems challenges at scale
.

WHY ENGINEERS ARE JOINING THIS TEAM

The tech stack will make you excited to code.
Scala with cats-effect, event sourcing with Kafka, microservices on AWS—this isn't legacy infrastructure. You'll work with modern FP patterns and have input on technical decisions.

Never touched functional programming? Perfect.
Several engineers joined without FP experience and learned through pair programming and team collaboration. You'll have mentorship, learning time, and a team that wants to help you grow.

Your code goes straight to production.
No bureaucracy, no endless approval chains. Build features, see them launch, watch millions of users benefit. The feedback loop is immediate and addictive.

Work on problems that actually matter.
Real-time payment processing, fraud prevention, distributed transactions - these aren't toy problems. You're building systems that need to be secure, scalable, and reliable because actual money depends on them.

The team culture is genuinely collaborative.
Engineers from 35+ countries, knowledge sharing is the default, and your ideas get heard regardless of seniority. This isn't a place where junior engineers just implement tickets.

WHAT YOU'LL BUILD

• Develop backend services for payment platform infrastructure (security, reliability and performance are non-negotiable in fintech)
• Collaborate with product teams to shape features from concept to production,
  making architectural decisions
  that matter.
• Work in cross-functional teams shipping payment capabilities that
  go live immediately
  for merchants and consumers.
• Design systems balancing speed, scalability, and maintainability while meeting strict compliance requirements.
• Participate in code reviews where learning flows both ways

WHO YOU ARE

Technical foundation:

• Proficient in statically-typed languages (
  Scala
  , Kotlin, Rust, Haskell) with curiosity about
  functional programming
• Write quality, readable code and approach debugging systematically
• Understand automated testing, software architecture, and basic security implications
• Comfortable with Git, team collaboration, and knowledge sharing across functions
• Connect engineering decisions to business goals—you care about the "why" behind your work
• Manage ambiguity well and bring entrepreneurial energy to a growth-stage environment
• Work Authorization:
  Japan-based or valid Japanese work visa required

BONUS EXPERIENCE (NOT REQUIRED)

• Our tech stack:
  Scala, Cassandra, Kafka, Postgres, REST APIs, microservices, event sourcing, cats-effect, AWS, Terraform, distributed systems
• Payment platforms or fintech experience
• Understanding of cross-team dependencies and product thinking
• Experience with cloud platforms, especially AWS

THE TECH & ENVIRONMENT

Stack:
AWS (Fargate), Scala, cats-effect, Kafka, Cassandra, Postgres, Elasticsearch, Redis, Docker, Terraform, CircleCI

Architecture:
Microservices, event sourcing, CQRS patterns, RESTful APIs, distributed systems

Team:
International engineers from 35+ countries in a rapid-growth environment

Work model:
Hybrid—central Tokyo office twice weekly, full flexibility otherwise, no core hours

WHAT MAKES THIS DIFFERENT

You'll actually learn functional programming on the job.
This isn't just lip service—the team actively mentors engineers new to FP concepts through pairing and gradual adoption.

Direct impact visibility.
Your code enables transactions for Japan's largest e-commerce merchants. You'll see the results of your work in production immediately.

Modern engineering practices.
Automated testing, CI/CD, infrastructure as code, code reviews—all the things that make development enjoyable are standard here.

Room to grow technically.
Whether you want to go deep into distributed systems, become an FP expert, or explore fintech-specific challenges, the opportunities exist.

International environment in Tokyo.
English-friendly workplace where diverse perspectives drive better technical solutions.

INTERESTED? LET'S TALK

Send your CV to

— all conversations completely confidential.

Even if you're not actively looking, if this tech stack and these problems excite you, reach out. Sometimes the best opportunities are the ones you weren't expecting.