Senior Software Engineer, Platform API - Ruby on Rails

Senior Software Engineer, Platform API - Ruby on Rails Treasure AI: Treasure AI is the agentic experience platform built to acquire, retain, and grow your most valuable customers. Powered by AI, Treasure AI is shaped by human creativity and always-on through continuous, context-driven action. Furthermore, Treasure AI employees are enthusiastic, data-driven, and customer-obsessed. We are a team of drivers—self-starters who take initiative, anticipate needs, and proactively jump in to solve problems. Our actions reflect our values of honesty, reliability, openness, and humility. Work the team does, and you will participate in: Design, ship, and operate Ruby on Rails Platform APIs end-to-end—from spec to rollout—meeting agreed availability/latency SLOs. Drive API design (OpenAPI/contract tests), versioning/deprecation, and compatibility for first-party UIs and partner integrations. Operate across the stack as needed, from backend APIs to front-end experiences, based on product needs. Ensure scalability, performance, and operationalization remain primary concerns throughout development. Keep up to date on novel technical concepts that we should adopt (and which ones we should ignore). Evaluate and introduce pragmatic improvements (framework/library upgrades, testing strategy, CI/CD/IaC) with clear trade-offs—in writing. Your experience and skills will include: 5+ years of software engineering experience with a proven track record. Have the ability to work full-stack (from the DB all the way to the Frontend). Writing Web APIs in Ruby on Rails. SQL and working with and maintaining Relational Databases in a production environment. System architecture and design Knowledge of design patterns involving APIs that communicate with many backend components. Variety of testing approaches, correctness through design, and a holistic approach to quality. Cloud technologies (particularly AWS) and development/deployment in a cloud infrastructure. Write clear design docs and incident postmortems; communicate across time zones. Comfortable working in English and Japanese: can participate in team meetings, ask/answer questions, and write simple tickets/Slack messages in either language. We would be thrilled if you had: Sense of project ownership and responsibility. Experience owning and leading short to medium-term technical direction across teams Business-level English proficiency and conversational-level Japanese proficiency Experience working in a different programming environment, such as the JVM (Java or Kotlin) or a different API style, such as JSON: API. Contributed to a production-grade web application handling high traffic. Experience in developing a fully managed cloud service. Experience with microservices-oriented architectures and authentication/authorization challenges. Made open source contributions. Physical Requirements: 3 days in Treasure AI Office Our Dedication to You: We value and promote diversity, equity, inclusion, and belonging in all aspects of our business and at all levels. Success comes from acknowledging, welcoming, and incorporating diverse perspectives. Diverse representation alone is not the desired outcome. We also strive to create an inclusive culture that encourages growth, ownership of your role, and achieving innovation in new and unique ways. Your voice will be heard, and we will help amplify it. Agencies and Recruiters: We cannot consider your candidate(s) without a contract in place. Any resumes received without having an active agreement will be considered gratis referrals to us. Thank you for your understanding and cooperation! Department Engineering | R&D Role Senior Software Engineer Locations Tokyo, Japan Remote status Hybrid Employment type Full-time About Treasure AI Treasure AI moves marketing and data teams beyond legacy martech SaaS toward autonomous, ROI-driven AI agents that operate continuously, while keeping the human in the loop. With built-in governance, Treasure AI is powered by an always-up-to-date understanding of each customer for AI to act on. The result is always-on marketing execution that compounds over time: smarter engagement, stronger retention, and measurable growth. Treasure AI’s agentic experience platform is available across web, mobile, and desktop — bringing your customer intelligence to every workflow, wherever your team works. Founded in 2011 Coworkers 560