01About

Hi, I'm Eiji Mitsumizo

I studied Mathematical Sciences with a specialisation in Cryptography, and discovered programming in a Java class during my 1-year CS exchange at the University of Oklahoma — math led me to cryptography, and cryptography led me to code.

Five years in EdTech at Benesse: I built my foundation on large-scale, mission-critical backends, solo-built the Java backend of one of Japan's first production EdTech generative-AI products, then founded Shinkenzemi √Route as its first engineer — scaling the team from 1 to 26 while serving as PM & Tech Lead. In my final role I reported directly to the CIO, solo-building an AI content pipeline with Claude Code + Codex, and left Benesse in July 2026. I'm now shipping a full-stack TypeScript hiring marketplace end-to-end — design through operations — as a solo contract engineer.

My motto: technology is a means — purpose comes first. The greatest reward is the act of building something new. And the measure I design by is longevity: what I build should keep running without me.

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Sydney

India

China

Australia

Speaking

Countries Visited

Japan
Philippines
USA
Canada
South Korea
Singapore
India
Australia
Germany
Taiwan
China

Years of Experience

0-to-1 Launches

Team Scaled (1→26)

30×

API Speedup (in-memory)

02Values & Philosophy

"Enrich someone's heart" — the drive I built over five years in EdTech. If a service makes people happy and hopeful, the domain doesn't matter.

An engineer who works globally and champions people's dreams, across any country or culture.

Five Values I Hold

Growth

I grow the most in new environments and challenges.

Going Global

Rooted in study abroad in the US and the Philippines — living among diverse values.

Technology

I don't cling to programming; I choose technology by working backwards from the value I want to deliver.

Product

0→1 building. Making someone's life better with something I created.

Human Connection

Standing beside each person and supporting my teammates' growth.

How I Work

Technology is a means; purpose comes first

Passed on Vue.js and chose React — working backwards from native-deployment potential and how well it pairs with AI-driven development.

Business outcome over sunk cost

Deliberately scrapped my self-built RAG when Claude Code / Codex arrived, replacing it in one to two weeks (AI SQL knowledge system).

The real problem always lives with the user

√Route weekend user meetups: observe in the morning, fix at noon, re-verify in the afternoon — a same-day improvement loop.

Write smart; crystallise it

It started with cleaning up legacy assets, and I hold AI to the same discipline.

Build solo, collaborate proactively

Solo-built the content pipeline while reaching out to the legal and content-production teams myself.

What I build keeps running without me (longevity)

Turning training into a lasting tradition / √Route running on its own after handoff / the SQL platform operated independently by the field team.

My Strength Equation

Engineering × Global Experience × Empathy for People

03Milestones

A journey of learning and growth.

2016Education

Entered Yamaguchi University

Enrolled in the Department of Mathematical Sciences. Drawn to cryptography, entering the world of math and programming.

2016Education

Entered Yamaguchi University

Enrolled in the Department of Mathematical Sciences. Drawn to cryptography, entering the world of math and programming.

2017-2019Education

Language Study in the Philippines (×3)

Three trips during university breaks from 2017, from English basics to IELTS prep. TOEIC jumped from 300 to 800.

2017-2019Education

Language Study in the Philippines (×3)

Three trips during university breaks from 2017, from English basics to IELTS prep. TOEIC jumped from 300 to 800.

2019.07Education

Exchange at University of Oklahoma

A department-first, risk-it-all challenge. Studied Math & CS for a year and discovered programming in my first Java class.

2019.07Education

Exchange at University of Oklahoma

A department-first, risk-it-all challenge. Studied Math & CS for a year and discovered programming in my first Java class.

2019-2020Achievement

Top 10 at a Hackathon

Entered as a duo with a friend and placed in the top 10 — my first taste of building something.

2019-2020Achievement

Top 10 at a Hackathon

Entered as a duo with a friend and placed in the top 10 — my first taste of building something.

2019-2020Personal

Volunteering with Alpha Phi Omega

As a member of the APO fraternity, volunteered to support homeless people and children.

2019-2020Personal

Volunteering with Alpha Phi Omega

As a member of the APO fraternity, volunteered to support homeless people and children.

2020Career

Founded a Study-Abroad Student Org

Founded after returning home, growing it from 3–4 to 15–16 members. Pivoted to online international exchange during the pandemic.

2020Career

Founded a Study-Abroad Student Org

Founded after returning home, growing it from 3–4 to 15–16 members. Pivoted to online international exchange during the pandemic.

2021.03Education

Graduated from Yamaguchi University

Graduation research on cryptography.

2021.03Education

Graduated from Yamaguchi University

Graduation research on cryptography.

2021.04Career

Joined Benesse Corporation

Started my engineering career, contributing to a large-scale shared membership platform.

2021.04Career

Joined Benesse Corporation

Started my engineering career, contributing to a large-scale shared membership platform.

2022Achievement

Breakthrough in Production

In year two, single-handedly took a mission-critical API from requirements to release. Sped up a nationwide API ~30× with an in-memory cache.

2022Achievement

Breakthrough in Production

In year two, single-handedly took a mission-critical API from requirements to release. Sped up a nationwide API ~30× with an in-memory cache.

2023Career

First Tech Lead / In-House Training

Became a tech lead in year three, leading a ~50-API PHP-to-Java migration and running new-grad training in-house.

2023Career

First Tech Lead / In-House Training

Became a tech lead in year three, leading a ~50-API PHP-to-Java migration and running new-grad training in-house.

2024.03Achievement

Challenge AI Learning Coach — Nationwide Launch

Nationwide launch of one of Japan's earliest EdTech generative-AI products, with a national TV commercial.

2024.03Achievement

Challenge AI Learning Coach — Nationwide Launch

Nationwide launch of one of Japan's earliest EdTech generative-AI products, with a national TV commercial.

2024-2025Achievement

Built √Route 0→1

Launched a learning service for high schoolers from scratch. Scaled the team from 1 to 26, turned monthly-profitable within 3 months, and won an internal global award.

2024-2025Achievement

Built √Route 0→1

Launched a learning service for high schoolers from scratch. Scaled the team from 1 to 26, turned monthly-profitable within 3 months, and won an internal global award.

2025Career

Founded the AI Agent Office / TOEIC 865

Founding member of the AI Agent Office, driving company-wide AI adoption. Reached TOEIC 865.

2025Career

Founded the AI Agent Office / TOEIC 865

Founding member of the AI Agent Office, driving company-wide AI adoption. Reached TOEIC 865.

2025.10Career

Solo-Built a Recruiting Marketplace

As a contract engineer, began solo-building Remote Crowd, a full-stack TypeScript recruiting marketplace (beta Feb 2026, public launch Jul 2026).

2025.10Career

Solo-Built a Recruiting Marketplace

As a contract engineer, began solo-building Remote Crowd, a full-stack TypeScript recruiting marketplace (beta Feb 2026, public launch Jul 2026).

2026.02Achievement

Patent JP 7815525 Granted

Granted a patent for a learning-support system (as co-inventor).

2026.02Achievement

Patent JP 7815525 Granted

Granted a patent for a learning-support system (as co-inventor).

04Skills & Technologies

The skills I've built in production — shown by years, proficiency, and what I've shipped.

Java / Spring Boot

Backend

4yr

Designed shared packages; operated high-traffic APIs in production.

TypeScript

Backend

1yr+

Shipped a commercial SaaS as a full-stack TypeScript engineer.

Python / FastAPI

Backend

3yr

Centred on AI platforms and data pipelines.

Next.js / React

Frontend

2yr

Doubled as the BFF layer on √Route; Atomic Design.

Azure

Cloud

4yr+

Deep production use of Functions, Cosmos DB, Web Apps, Queue, and AI Search.

AWS / Terraform IaC

Cloud

1yr

Build and operate App Runner / S3 / Lambda on Terraform IaC in a contract project (Terraform at a foundational level).

Claude Code + Codex

1yr+

Established a production dev workflow internally; 3 talks, one to executives.

OpenAI / Vertex AI

2yr+

Production AI product integration at work.

RAG

Built with Azure AI Search + Embeddings + pgvector, then deliberately retired — a pivot call.

LangGraph

Node-level implementation experience (no design-level decisions yet).

Databricks

Used in the current content pipeline.

In-Memory Cache Design

Data

~30× improvement via a read-heavy / write-rare DTO cache design.

Redis

Data

Fallback design that absorbs traffic during failover.

DB Index / Query Tuning

Data

4yr

SQL Server focus; one year of PostgreSQL.

Layered Architecture

Architecture

√Route's 3-language split, 3-layer pipeline, and Clean Architecture.

Application Security

Security

IDOR / CSP / auth — hardened a commercial SaaS solo.

CI/CD

DevOps

3yr

GitHub Actions / Azure DevOps; pipeline design on √Route and AI Tutor.

jMeter

Testing

3yr

Owned load testing end-to-end: planning, execution, analysis.

Team Scaling

Organisation

Scaled a team from 1 to 26 on √Route.

Curriculum Design / Instructor Training

Organisation

Built a 30-person, 2-month programme 0→1 and trained ~25 instructors.

Internal AI Evangelism & Talks

Organisation

Three talks to 50 people each, plus executives and 10+ teams.

English

Language

Professional working proficiency. TOEIC 865; one-year CS exchange at the University of Oklahoma.

05Professional Experience

Five years at Benesse in four phases — from backend foundations to 0-to-1 founding to AI strategy — plus full-stack work on the side.

Benesse Corporation

Apr 2021 – Jul 2026·Tokyo, Japan (Hybrid)

Apr 2021 – Jul 2023

Phase 1 — Backend Engineer → Tech Lead

30× SpeedupTech LeadZero Downtime

Started with the cloud migration of a large membership platform handling personal data. Built my engineering foundation on mission-critical API design and delivery, becoming a tech lead in my third year.

Key Achievements:

Designed and tested a per-error-type Redis fallback for the membership platform's cloud migration, absorbing traffic during momentary DB outages — as a team, zero downtime for 4+ years
Solo-delivered a mission-critical API (tablet initial setup for all subscribers) from requirements to release in my second year; built an in-house automated test tool to refactor legacy safely, with zero regression bugs
~30× faster video-listing API under large-scale daily traffic, via an in-memory DTO cache designed for read-heavy / write-rare access; zero-defect release
First tech lead in year three: migrated ~50 APIs from PHP to Java, structurally ensuring quality via a shared package design and cutting the WBS by ~30% (combined effect of shared packages and review efficiency); the PR-review workflow I proposed later became a company-wide standard
Solo-designed and built a consent-management API used by a large member base

JavaSpring BootAzureSQL Server

Aug 2023 – Mar 2024

Phase 2 — AI Product Engineer — AI Learning Coach

Nationwide LaunchZero Defects

Solo-built the Java backend of Shinkenzemi's 'Challenge AI Learning Coach' (a generative-AI chat for grades 4–9). Shipped one of Japan's earliest EdTech generative-AI products bug-free in 7 months with a 3-person team.

Key Achievements:

Nationwide launch in March 2024 (featured in a national TV commercial); among Japan's first production EdTech generative-AI products
Built the Java backend API end-to-end solo, from requirements through load testing (request shaping, usage-rate limiting, logging, master data); bug-free release with a 3-person team over 7 months
Supported the AI platform side with prompt design and evaluation tooling

JavaSpring BootAzureFastAPI

Highlight

Apr 2024 – Mar 2025

Phase 3 — Founding Engineer → PM & Tech Lead — Shinkenzemi √Route (Benesse internal 0-to-1 venture)

Founding EngineerTeam 1→26Profitable in 3 Months

Founded Shinkenzemi √Route from scratch — a new online learning platform for high schoolers built for university-entrance reform. Scaled from a solo prototype to a 26-person cross-functional team while serving as PM & Tech Lead.

Key Achievements:

Launched a 0-to-1 online learning platform for high schoolers; scaled the team from 1 to 26 while serving as PM & Tech Lead
Designed, proved, and adopted a three-language architecture (Next.js × Java × Python), split by responsibility, rate of change, and scope
Designed transactional payment integration across 8 independent internal systems with rollback strategies — zero billing defects since launch
Solo-implemented an AI self-talk learning feature with a responsible-AI design: the LLM selects from pre-vetted response candidates instead of generating freely, structurally containing hallucination risk
Reached monthly profitability within 3 months of launch; won an internal global award

Next.jsJavaPythonAzureOpenAI API

Apr 2025 – Jul 2026

Phase 4 — AI Engineer / Architect — AI Strategy & AI-First Engineering

CIO DirectPatent Co-inventor10+ Teams

Founding member of the AI Agent Office driving company-wide AI adoption. In my final phase I reported directly to the CIO, solo-building an educational content pipeline with Claude Code + Codex.

Key Achievements:

Founding member of the AI Agent Office: triaged AI-adoption requests across 10+ teams; grew a grassroots AI workshop from 2–3 to 20+ regular participants in 4 months
Supported the AI Tutor generative-AI learning product (LangGraph node implementation, load testing, proposing an event-driven architecture migration). Co-inventor on the granted learning-support-system patent JP 7815525 (registered Feb 6, 2026; 1 of 5 inventors, assigned to Benesse). The product won the Google Gen AI Innovation Grand Prize (a product-level award)
AI-powered SQL knowledge system: brought previously vendor-dependent SQL creation in-house with AI. Deliberately discarded my self-built embedding RAG (Azure AI Search + pgvector) once Claude Code / Codex arrived, pivoting to a platform-native approach (business outcome over sunk cost) — eliminating outsourcing costs
Educational content pipeline (reporting to the CIO; engineering solo, project led by 2 PdMs): a 3-layer LLM pipeline (Extract → Structure → Meta-tag) structuring 20,000+ questions and linking them to exam records problem-by-problem for the first time; expanded from a math PoC to all subjects with no re-architecture
Established and rolled out an AI-driven development process company-wide: requirements → discuss with Claude Code → issue breakdown → TDD implementation → iterative Codex + Claude Code review; presented internally, including to executives

PythonClaude CodeCodexDatabricksLangGraph

remolabo Inc. (client project)

Oct 2025 – Present·Remote (Side Project)

Oct 2025 – Present

Full-Stack Engineer — Solo Contract Engineer

Solo Full-StackB2B SaaS Launched

Solo contract engineer for Remote Crowd, a two-sided marketplace connecting remote workers with vetted companies (B2B subscription; beta Feb 2026, public launch Jul 2026), owning design, implementation, infrastructure, operations, and security single-handedly.

Key Achievements:

Shipped a commercial SaaS solo from design through operations: Next.js 14 + NestJS (Clean Architecture on both front and back), Turborepo monorepo
Managed PostgreSQL + Prisma and AWS (App Runner, S3, Lambda) via Terraform IaC
Implemented feature gating for a 3-plan subscription and an admin console (KPI dashboard, audit logs, CSV export)
Solo-implemented security hardening: IDOR protection, nonce-based CSP, account-enumeration defence, session invalidation on password change, admin email OTP 2FA, log sanitisation
Change-detection-based selective deployment; trunk-based development with ADRs

Next.jsNestJSPostgreSQLAWSTerraform

06Patents & Awards

Verifiable public records.

Patent

Learning-Support System (JP Patent 7815525)

Granted Feb 6, 2026

Co-inventor (1 of 5 inventors; assignee: Benesse Corporation). Described within the scope of the public patent gazette.

Award

Google Gen AI Innovation Grand Prize

AI Tutor (generative-AI learning product)

A product-level award.

07Education

B.S. in Mathematical Sciences (Cryptography)

Yamaguchi University, Faculty of Science

2016 – 2021

Specialised in cryptography within the Department of Mathematical Sciences. Studied for five years, including a one-year exchange abroad, building a strong foundation in mathematical thinking and logical problem-solving.

Highlights:

Graduation research in cryptography
Philippines language study: TOEIC 300 → 800
Self-taught web development with React & TypeScript
Founded a student organisation supporting study-abroad students

Exchange Programme (Math & Computer Science)

University of Oklahoma

Jul 2019 – Jun 2020

One-year CS exchange in the USA. Studied Math & Computer Science and earned full credits. 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 programming in my first Java class
Alpha Phi Omega — 10 months volunteering to support children
Substantially improved English proficiency through a year of overseas study

Certifications

TOEIC 865Azure Fundamentals (AZ-900)Fundamental Information Technology Engineer (FE)

Hi, I'm Eiji Mitsumizo

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