Hi, I'm Eiji Mitsumizo
I want to build a society where people can proactively live with joy and pursue their dreams. I'm endlessly curious, love food, travel, and different cultures. I thrive on building things from scratch and find the greatest joy in achieving something big with a team. I believe in a future where AI and humans work together, and see it as my mission to expand what people can do through technology. With this passion, I'm seeking new challenges in Europe.
Japan → Europe
Eiji
Building Ideas
Building Ideas
Exploring
Exploring
Tech Life
Tech Life
0K+
AI Product Users
$0M+
Revenue Generated
0+
Production Systems
0%
Cost Reduction
Engineering Principles
The principles that guide how I build software every day.
Simplicity Over Complexity
I favour straightforward solutions over clever abstractions. Code should be easy to read, review, and maintain.
Ship, Measure, Iterate
I believe in getting working software into users' hands quickly, measuring real impact, and iterating based on data.
AI-Augmented Development
I actively integrate AI tools like Claude Code and LangGraph into my workflow to write better code faster and automate repetitive tasks.
Milestones
A journey of learning and growth.
2016Education
Entered Yamaguchi University
Enrolled in the Department of Mathematical Sciences. Developed an interest in cryptography and entered the world of math and programming.
2016Education
Entered Yamaguchi University
Enrolled in the Department of Mathematical Sciences. Developed an interest in cryptography and entered the world of math and programming.
2017-2018Education
Study Abroad in the Philippines
Three trips during university breaks from 2017. TOEIC score jumped dramatically from 300 to 850.
2017-2018Education
Study Abroad in the Philippines
Three trips during university breaks from 2017. TOEIC score jumped dramatically from 300 to 850.
2018-2019Education
Exchange at University of Oklahoma
Studied Math & Computer Science for one year. Joined Alpha Phi Omega as the only international student, volunteering for 10 months.
2018-2019Education
Exchange at University of Oklahoma
Studied Math & Computer Science for one year. Joined Alpha Phi Omega as the only international student, volunteering for 10 months.
2020Achievement
Dove Deep into Programming
Started self-learning web application development. Mastered React and TypeScript.
2020Achievement
Dove Deep into Programming
Started self-learning web application development. Mastered React and TypeScript.
2020Achievement
Achieved IELTS 6.0
Result of overseas experience and continuous learning.
2020Achievement
Achieved IELTS 6.0
Result of overseas experience and continuous learning.
2021Education
University Graduation -- Cryptography Major
Completed research in cryptography & zero-knowledge proofs. Founded SOAR (study abroad support organisation).
2021Education
University Graduation -- Cryptography Major
Completed research in cryptography & zero-knowledge proofs. Founded SOAR (study abroad support organisation).
2021Career
Joined Benesse Corporation
Started career as a full-stack engineer. Built high-availability infrastructure for the core personal data platform.
2021Career
Joined Benesse Corporation
Started career as a full-stack engineer. Built high-availability infrastructure for the core personal data platform.
2022Career
Kodomo Challenge Platform Renewal
Led API development for a service used by 2M+ households. Achieved 30x API response speedup via cache architecture.
2022Career
Kodomo Challenge Platform Renewal
Led API development for a service used by 2M+ households. Achieved 30x API response speedup via cache architecture.
2023Career
Shimajiro Club Migration & AI Learning Coach
Led legacy migration + shipped one of Japan's earliest EdTech generative AI products in 7 months with a 3-person team. ¥100M PR value.
2023Career
Shimajiro Club Migration & AI Learning Coach
Led legacy migration + shipped one of Japan's earliest EdTech generative AI products in 7 months with a 3-person team. ¥100M PR value.
2024Career
√Route Launch
Built a 0→1 learning platform. 7,000+ paid users in 4 months, $1M+/yr revenue. AES GLOBAL AWARD Bronze.
2024Career
√Route Launch
Built a 0→1 learning platform. 7,000+ paid users in 4 months, $1M+/yr revenue. AES GLOBAL AWARD Bronze.
2025Career
AI Agent Development Office
Technical consultant & AI evangelist for 700+ staff. AI Tutor reached 50,000 users -- Google Gen AI Innovation Grand Prize.
2025Career
AI Agent Development Office
Technical consultant & AI evangelist for 700+ staff. AI Tutor reached 50,000 users -- Google Gen AI Innovation Grand Prize.
2025Achievement
TOEIC 865
Result of continuous learning.
2025Achievement
TOEIC 865
Result of continuous learning.
2025Career
System Knowledge AI -- SQL Auto-Generation
Transforming manual SQL workflows into AI knowledge system. Pivoted from custom RAG to Claude Code/Codex. ¥40M/yr projected savings.
2025Career
System Knowledge AI -- SQL Auto-Generation
Transforming manual SQL workflows into AI knowledge system. Pivoted from custom RAG to Claude Code/Codex. ¥40M/yr projected savings.
2025Career
Data Pipeline & AI Data Strategy
Solo architect under CIO. Structuring education documents (PDFs) into structured JSON for company-wide generative AI applications.
2025Career
Data Pipeline & AI Data Strategy
Solo architect under CIO. Structuring education documents (PDFs) into structured JSON for company-wide generative AI applications.
Skills & Technologies
Tools and technologies I use to build production systems.
TypeScript
Frontend0yr
2 projects
Primary language for full-stack development
React
Frontend0yr
2 projects
SPA to SSR, component-driven UIs
Next.js
Frontend0yr
2 projects
App Router, Server Components. Used in √Route etc.
Java
Backend0yr
10 projects
Primary language since joining Benesse. Also teach in training programs.
Spring Boot
Backend0yr
10 projects
Enterprise systems, 5 years production use
Python
Backend0yr
5 projects
FastAPI, AI integration, data pipelines
FastAPI
Backend0yr
5 projects
AI-integrated Python APIs with Azure OpenAI
SQL Server
Database0yr
Primary DB. Index tuning, performance optimization.
PostgreSQL
Database0yr
2 projects
Vector search and recent projects
Redis
Database0yr
Cache layer. Achieved 30x API response speedup.
Azure
Cloud0yr
8 projects
App Service, SQL Database, DevOps, Functions
AWS
Cloud0yr
2 projects
Cloud for side projects
Vercel
Cloud0yr
Next.js deployment & edge
Terraform
Cloud0yr
Infrastructure as Code
LangGraph
AI / ML0yr
3 projects
Multi-agent orchestration framework
Azure OpenAI
AI / ML0yr
3 projects
Production AI integration for learning products
Claude Code
AI / ML0yr
AI-powered development workflow. $200/mo personal spend.
Cursor
AI / ML0yr
AI-assisted IDE, used alongside Claude Code
jMeter
Testing / CI0yr
Load test planning, execution & analysis
CI/CD
Testing / CI0yr
GitHub Actions, Azure DevOps
English
LanguageIELTS 6.0 + TOEIC 865 -- study abroad in US & Philippines
Professional Experience
5 years, 8 roles, one company -- driving impact at scale.
Benesse Corporation
Apr 2021 -- PresentTokyo, Japan (Hybrid)
2025 -- Present
Data Pipeline & AI Data Strategy -- Solo Architect
Solo ArchitectCIO Direct
Designing and building an end-to-end data pipeline under the CIO, structuring massive unstructured education documents (PDFs) into structured JSON for company-wide generative AI applications.
Key Achievements:
- Architected layer-based pipeline: extraction → structuring → meta-tagging → JSON
- Managed cross-department stakeholders, translating AI requirements into domain language
- Leveraging Claude Code to deliver solo from requirements through production
PythonDatabricksClaude Code
2025
System Knowledge AI -- Lead Engineer
¥40M/yr Savings
Transforming costly, person-dependent SQL generation workflows into an AI knowledge system. Pivoted from custom RAG to Claude Code/Codex platform-native approach.
Key Achievements:
- Projected ¥40M/yr ($270K) cost savings through AI-driven SQL automation
- Built and intentionally discarded custom RAG system in favour of Claude Code/Codex
- Designed extensible custom command/skill architecture for new knowledge domains
Claude CodeCodexPostgreSQLPython
2025
AI Agent Development Office -- Tech Consultant & Evangelist
50,000 UsersGoogle Award
Central AI advisory point for 700+ staff across 10+ teams. Provided trend analysis, feasibility assessment, and hands-on architecture & implementation support.
Key Achievements:
- AI Tutor: Proposed cross-team unified product → 50,000 users, Google Gen AI Innovation Grand Prize
- Consolidated duplicate AI development across teams, reducing cloud costs by 40%
- Ran company-wide AI literacy workshops, improving non-engineer productivity by 20%
PythonLangGraphAzure FunctionsjMeter
2024 -- Present
√Route -- Solo Founding Engineer → PdM (26-person team)
7,000+ Paid Users$1M+/yr RevenueAES Award
Led 0→1 development of a high-school learning platform. Scaled from solo prototype to 26-person cross-functional team, bringing the product to profitability.
Key Achievements:
- 7,000+ paid users in 4 months, $1M+/yr revenue, ahead-of-schedule profitability
- AES GLOBAL AWARD Bronze for innovative "Self-Talk" feature
- Transitioned from coding to full PdM: stakeholder management, requirements, UX oversight
Next.jsSpring BootAzureCI/CD
2023 -- 2024
Engineer Training Program -- Lead
67% Cost Reduction
Led Benesse's first in-house onboarding program. Designed a 2-month practical curriculum and coached 20 junior engineers as internal instructors.
Key Achievements:
- 67% training cost reduction: ¥30M → ¥10M ($133K/yr saved)
- Designed Java/Python/HTML curriculum for 30 new engineers
- Achieved 4.70/5 trainee satisfaction; standardised reusable materials
JavaPythonHTML/CSS/JS
2023
Shimajiro Club Migration & AI Learning Coach
¥100M PR Value
Led legacy system migration and built one of Japan's earliest EdTech generative AI products. Shipped in 7 months with a 3-person team.
Key Achievements:
- Zero-defect Java backend API release; FastAPI + OpenAI Python API for AI interactions
- Designed reusable API components, reducing team development time by 30%
- Generated ¥100M ($670K) PR value through major media coverage
PythonFastAPIAzure OpenAIJava
2022 -- 2023
Kodomo Challenge Platform Renewal -- Performance Lead
2M+ Households30x Speedup
Led API development and performance optimisation for Kodomo Challenge, serving 2M+ households nationwide. Handled mission-critical APIs processing 1M+ daily requests.
Key Achievements:
- 30x API response speedup via cache architecture; zero-defect release
- Built mission-critical APIs handling 1M+ daily requests (~3,000K steps)
- Conducted full load test lifecycle with jMeter (planning, execution, analysis)
JavaSpring BootSQL ServerRedis
2021 -- 2022
Personal Data Platform -- Infrastructure Engineer
Zero Downtime
Built and evolved high-availability infrastructure for the core personal data platform. Grew from first production project to solo interface renovation.
Key Achievements:
- Implemented Redis cache layer handling 40% of requests during SQL Server failover; zero downtime since launch
- Proposed Reserved Instance strategy via load testing, significantly reducing infra costs
- Solo end-to-end interface renovation (requirements → design → implementation → release)
JavaSpring BootRedisAzure
Education
B.Sc. Mathematical Sciences (Cryptography)
Yamaguchi University
2016 -- 2021
Majored in cryptography in the Department of Mathematical Sciences. Built a strong foundation in mathematical thinking and logical problem-solving.
Highlights:
- Cryptography & zero-knowledge proof research
- Philippines study abroad: TOEIC 300 → 850
- Self-taught web development with React & TypeScript
- Founded SOAR (study abroad support organisation)
Exchange Programme (Math & Computer Science)
University of Oklahoma
2018 -- 2019
One-year exchange programme. Studied Math & Computer Science. Joined Alpha Phi Omega as the only international student, volunteering for 10 months.
Highlights:
- Studied mathematics and CS courses in English for one year
- Discovered Computer Science and programming
- Alpha Phi Omega -- 10 months of children's support volunteering
- Achieved IELTS 6.0 through continuous English study