Principal Engineer (Founding Engineer)

About Rakuda AI

Rakuda AI is a Tokyo-based product studio that designs, builds, and operates AI-powered web applications, e-commerce platforms, and business-process automation systems. We deliver full-stack products end-to-end — frontend, backend, infrastructure, and LLM integration — entirely in-house, with no external subcontracting.

Our founders are serial entrepreneurs:

• Masaki Arakawa (Representative Director): Keio University. Founder of Amy Inc., a software-development and marketing-support company, which he successfully exited through a sale to Vector Inc. (Tokyo Stock Exchange Prime-listed).
  
  
• Yudai Futai (Co-founder): Kyoto University, Faculty of Economics. Former e-commerce consultant at Rakuten, Manager of Business Development at IoT startup Qrio, and co-founder of scouty (now LAPRAS Inc.), a leading Japanese AI HR-tech company.

We ship production-grade products on aggressive timelines — typically 1 to 1.5 months for a full build. Recent work includes a marketplace platform shipped in one month, an LLM/RAG document-analysis system for a fintech, and AI feature integration for a B2B SaaS in three weeks.

About the Role

We are hiring our first Principal Engineer / Founding Engineer to define the technical foundation of Rakuda AI as we scale from a senior-led studio into a category-defining AI product company.

This is not a "lead a team of mid-level engineers" role. We are looking for someone who can personally architect and ship the most demanding parts of our most demanding projects, while also setting the engineering bar for everyone we hire after them. The successful candidate will work side-by-side with the founders, with full authority over technology choices, hiring, and engineering culture.

We are targeting senior engineers currently at top global or Japanese tech firms at the Staff / Senior Staff / Principal level.

Responsibilities

• Own the technical architecture across all client engagements: AI-integrated web applications, e-commerce platforms, and internal business systems
• Personally implement the highest-leverage parts of each system — LLM/agent infrastructure, performance-critical backends, AI evaluation pipelines
• Set engineering standards: code review, architecture review, language and framework choices, infrastructure and security baselines
• Hire and develop the engineering team alongside the founders
• Work directly with founders and senior client stakeholders to shape product direction
  
  

Requirements

• 5+ years of professional software engineering experience, including at least 3 years at Staff / Senior Staff / Principal level (or equivalent) at a top-tier engineering organization
• Demonstrated track record of personally architecting and shipping production systems at scale
• Deep full-stack proficiency: TypeScript and at least one modern JS framework (Next.js, React, or equivalent), plus strong backend, database, and cloud infrastructure (AWS, GCP, or equivalent) skills
• Strong opinions on engineering quality, with the ability to set and enforce a high bar
• Business-level English (for technical communication, AI tooling, and engineering documentation)
• Business-level Japanese (for direct communication with Japanese clients and executives) — required
• Based in Japan and able to work full-time on-site at our Tokyo office
  
  

Strongly Preferred

• Hands-on production experience integrating LLMs (OpenAI, Anthropic Claude, etc.), including RAG pipelines, vector databases, evaluation, and agent frameworks
• Prior experience as a founding engineer, principal engineer, or technical co-founder at a startup
• Experience working directly with C-level stakeholders or as a technical decision-maker
• Open-source maintainer experience or recognized technical writing / speaking
  
  

What We Offer

• Compensation: starting from JPY 30M base, with significant upside tied to the growth of the company (negotiable based on level and contribution)
• Direct collaboration with serial-entrepreneur founders with prior exits and operational track records
• Genuine founding-engineer authority: technology choices, hiring decisions, engineering culture
• AI-first engineering environment with full access to frontier AI tools (Claude, Cursor, OpenAI, internal tooling) as part of daily work
• Tokyo office in the central business core of the city
• On-site, in-person work — designed for high-velocity decision-making and deep collaboration

Working Style

This is an on-site role at our Tokyo office. We believe the best engineering work — particularly at the principal level, and particularly during this stage of the company — happens in the same room as the founders, the rest of the engineering team, and our clients. We do not offer remote work for this position.

Relevant Skills

TypeScript, Next.js, React, Node.js, AWS, GCP, PostgreSQL, LLM Integration, OpenAI API, Anthropic Claude API, RAG, Vector Databases, System Architecture, Full-Stack Development, REST API, GraphQL, Principal Engineer, Founding Engineer, Engineering Leadership