Backend Engineer, Ruby

KOMOJU Musashino-Shi, Tokyo April 3 2026
  • 💴 No salary range given
  • 🏡
    Fully remote
    From Japan
  • 🌏
    Apply from abroad
    Relocate to Japan
  • 💬
    No Japanese required
    Business English
  • 🧪
    Intermediate to senior levels
    Unspecified years of experience
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About KOMOJU

KOMOJU Musashino-Shi, Tokyo

The leading cross-border payment gateway for Japan. We power payments for companies like video game distribution platform Steam and the popular mobile app TikTok.

Key benefits

  • Developer-centric, inclusive culture
  • International at our core
  • Generous holiday policy

About the position

We are looking for a backend engineer to help us build our platform to handle payments on a global scale. You will primarily work with Ruby, building out features using Ruby on Rails (90% of tasks). As we’re still scaling our front-end team, you may be asked occasionally to work on front-end tasks as well (Less than 5% of tasks). As well as this there will be tasks related to Monitoring, Observability etc. which uses Terraform and DataDog (< 5%).

Typical tasks include adding new APIs for Front-end Interfaces in our Ruby on Rails application for customers to use, investigating bugs with our partners to ensure customer payments go through smoothly, and improving our systems’ reliability and observability to ensure better better health using Terraform.

You will work with our product managers and critically evaluate requirements then implement those requirements in code. You will also work with your fellow developers and provide constructive feedback through code reviews, look at refactoring opportunities, and helping improve the codebase. You will receive mentoring support from managers and senior developers to help develop your skills as realizing growth potential is a key goal.

Our ideal candidate has experience working with large web applications. They will know how to build reliable and performant web applications. Testing and code quality are also extremely important to us, so having a strong knowledge of testing and the different testing types is required.

Responsibilities

  • Build backend systems using Ruby on Rails stack.
  • Understand product goals and feature requests and translate them into working software
  • Work on large technical projects from design through implementation and delivery as part of a team
  • Ensure high-quality, reliable software - including thorough testing.

Requirements

- Strong experience building backend systems using Ruby on Rails in production environments (We prefer Ruby experience, but candidates with solid experience in other backend web frameworks are also welcome.) - Experience building scalable and performant web applications. - Solid understanding of relational databases and SQL - Ability to design data models and system architectures. - Strong technical communication skills - including the ability to document decisions clearly and concisely - Experience and understanding of common web vulnerabilities and how to mitigate them - Understanding of software architecture, design patterns, and best practices

Nice to haves

While not specifically required, tell us if you have any of the following.

- Experience with TypeScript, Vue.js, or React - Experience with payments or payment systems - Experience with integrating with third party APIs in a secure and fault-tolerant manner - Understanding of database performance characteristics and data access patterns - Familiarity with Monitoring and Observability techniques and platforms such as DataDog.

Hiring Process

  1. 1

    Initial screening call with HR

    To understand candidates’ overall professional background, career aspirations, and to evaluate the fit for the role/ culture.

  2. 2

    Take-home exercise

    It’s opportunity to evaluate candidates’ practical experience and observe that they follow best practices.This includes, but is not limited to, their coding skills, problem-solving abilities, system design capabilities and ability to optimize and maintain code. We normally give the applicant one week to complete it, but we don’t expect it to take more than 2 hours.

  3. 3

    Technical team interview

    This interview serves two purposes: it’s a chance to review the take-home exercise and assess the candidate’s technical abilities, and it also helps evaluate their soft skills, how well they collaborate with stakeholders and team members, manage their work (time management, prioritization, adaptability), and demonstrate a commitment to continuous learning.

  4. 4

    Final interview with leadership

    We’re looking here to assess culture add. We’re not looking for people that just fit the status quo (culture fit), we want candidates who can bring something new and valuable to our culture. While ensuring that they still align with our core values, we want to assess their ability to adapt to recent changes within the organization and to help guide the organization through its next stage of development.

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Meet KOMOJU's Developers

Kazunori initially joined KOMOJU as a web application engineer, but by identifying problems he wanted to fix, his role shifted first to VP of Infrastructure, and then VP of Payment Products.

Read their story...

Nicole joined KOMOJU in 2020, and worked her way up to be technical lead of the merchant management team. She shares her journey, how KOMOJU supported her career growth and how the company is adapting to its growing needs.

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Photo of Richard Ramsden

Becoming CTO of KOMOJU

with Richard Ramsden

After graduating from university, Richard came to Japan and found a job as a software developer. Eventually he joined KOMOJU, where he rose to the role of CTO.

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Nigel was fresh out of college when he joined KOMOJU as a developer. He's now risen to tech lead, where he's helped build out their payment platform while maintaining a healthy work-life balance.

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Muhammad Denaw, Senior Site Reliability Engineer at Komoju, talks about his work and shares how Komoju's trust and support propelled him to a promotion.

Read their story...

Head of Customer Engineering Makoto Mizukami describes the unconventional candidates his unique team is looking for.

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