01PORTFOLIO · 2026
Software Engineer
Engineering, research, and a stack of side projects — built over 20+ years.
02ABOUT
I'm a software engineer with over 20 years of experience building scalable systems and innovative solutions. Currently serving as CTO at Minedia, a data technology startup where we raised approximately ¥500M in funding. My career has spanned multiple high-growth companies including Metaps, where I led the development of SPIKE (a zero-fee payment service), and GREE, where I managed social gaming platform development.
I hold a degree from Keio University Shonan Fujisawa Campus (2005) and studied at UCLA Extension (2006). My approach combines deep technical expertise with strategic thinking, enabling me to build systems that drive business growth while maintaining high engineering standards.
03PERSONALITY
As an INTP-A (Assertive) type, I bring confidence and calm under pressure to technical leadership. My approach combines rigorous logical thinking with genuine care for team members' growth and development.
I excel at breaking down complex technical challenges, creating clear strategic roadmaps, and building environments where engineers can do their best work.
Note: Based on MBTI assessment and LLM analysis. Full Analysis
04RESEARCH
Published in Springer • 2023
Research analyzing e-commerce data to understand regional characteristics and consumer behavior patterns.
Master's Thesis, Keio University • 2005
Design and implementation of activity models using location information and place attributes for navigation services.
2023
Panel discussion about the future of data ecosystems with insights from Minedia's Mineds service.
CEDEC 2012
How to Develop Attractive Games for 1 Billion Users
CodeZine • April 15, 2011
Comprehensive comparison of various ORM libraries for PHP development, analyzing features and performance benchmarks. This article examines advantages and disadvantages to help architects select appropriate ORM libraries, covering improved database schema maintainability and reduced SQL dependency.
GREE Tech Blog • April 25, 2011 • 2,221 Hatena Bookmarks (All-time #1)
Detailed guide on adapting existing mobile websites for smartphones. Covers 8 steps from UTF-8/HTML5 conversion, jQuery Mobile integration, emoji replacement, to HTML5 validation. This article became the all-time most bookmarked post on GREE Tech Blog, demonstrating its significant impact on the Japanese developer community.
Patent No. 6755427 • Granted 2020 • Minedia, Inc.
An invention for a purchase-information system that collects and analyzes panelists' email data to extract product purchase information and grant rewards based on it. Registered as a co-inventor.
Patent No. 6676809 • Granted 2020 • Minedia, Inc.
An invention for a system, method, and program that efficiently support qualitative consumer research. Registered as a co-inventor.
05EXPERIENCE
Minedia, Inc.
Metaps, Inc.
GREE Inc.
06STACK
07WORK
Modern intelligent applications for real-world workflows
Highly Customizable Content Moderation System
A flexible content moderation system that enables selection of optimal LLMs based on specific use cases. Customers can freely configure system prompts and instructions for each organization, achieving moderation that perfectly aligns with industry-specific content guidelines and corporate policies. Employs a multi-model architecture that integrates multiple LLMs including OpenAI API in a unified management system. Flexibly switches between models with different characteristics—precision-focused, speed-focused, or cost-focused—depending on needs. Featured in Nikkei as an emerging moderation service, it differentiates itself through complete customizability, providing ideal solutions for niche industries and companies with specialized content requirements.
LLM-Powered Training Plans & Race Result Analysis Platform
A comprehensive LLM coaching platform built on a database of 2,444+ Japanese triathlon events, 3.5M+ race result records, and 1.25M+ athlete profiles—published as open source on GitHub. The race analysis engine generates rankings, percentile-based deviation scores, strength/weakness diagnostics, training advice, and race reviews. The LLM coach generates personalized training plans from 100+ data points, with periodization (base → specialty → competition → recovery), power/HR zone optimization, and dynamic adjustment based on fatigue and motivation. A 24/7 LLM chatbot answers coaching questions, and plans sync with Google/Apple Calendar via a drag-and-drop interface. A REST API with OpenAPI specification and MCP (Model Context Protocol) support exposes the platform's data to LLM assistants like Claude. Free tier offers race analysis and an initial plan; Premium adds unlimited goals, continuous plan regeneration, chat support, and performance prediction—at roughly 1/200 of traditional coaching pricing.
Offline-capable utility applications for outdoor activities
Summit locator for amateur radio operations
A Progressive Web App designed for SOTA (Summits On The Air) activators to identify and locate summits for amateur radio operations. Works offline with cached summit data, making it perfect for use in remote mountain locations without internet connectivity.
Ham radio grid square calculator
An offline-capable tool for amateur radio operators to calculate and convert QTH locators (Maidenhead grid squares) from GPS coordinates. Essential for VHF/UHF operations and contesting, with full functionality without internet connection.
Running pace and split time calculator
A comprehensive pace calculator for runners and triathletes. Calculate target paces, split times, and finish times for various race distances. Works completely offline, making it ideal for use during training runs and races.
Modern REST & GraphQL APIs for Japanese data
High-performance Japanese postal code lookup service
Japanese banking institution codes
Company registration information
Railway and station information
Educational institution database
Japanese dam database
Era ↔ Western calendar conversion
Japanese hanko/seal image generator
Open source tools I've built and maintain
Go CLI to transcribe macOS Voice Memos
A Go CLI tool (vmt) that transcribes macOS Voice Memos recordings using pluggable STT engines. Supports CLI, TUI, and Alfred Workflow interfaces. Ships with ElevenLabs Scribe.
Claude Code Max usage display for tmux/Starship
Displays Claude Code (Max Plan) API usage in your tmux status bar or Starship prompt. Shows 5-hour and 7-day utilization as compact, color-coded progress bars. Pure bash + jq + curl.
Notable service developments from my career
CTO / Tech Lead
Developed a platform to streamline online qualitative research. Built a system enabling user interviews, group discussions, and behavioral observations to be conducted online. Implemented real-time recording and analysis features to achieve DX in research operations.
Tech: Ruby on Rails, React, WebRTC, AWS
Development Lead
In response to city gas deregulation, developed a system for city gas retail application processing and integration with gas pipeline companies. Designed as a multi-tenant SaaS platform, enabling multiple retail operators to independently use the service while maintaining data isolation for each tenant and providing a shared functional foundation. Realized online workflow from application to gas meter opening.
Tech: Ruby on Rails, PostgreSQL, AWS, REST API, Multi-tenant SaaS
Development Lead
Developed a system to accept web-based product recall applications and integrate with multiple logistics companies. Implemented inventory coordination with logistics warehouses, delivery tracking, and automatic customer notifications. Built as a SaaS platform for multiple manufacturers.
Tech: Ruby on Rails, PostgreSQL, REST API Integration
Lead Engineer
Developed and launched from scratch in 3 months an innovative service with zero payment fees. Built a payment platform for EC businesses supporting credit cards, bank transfers, and convenience store payments. Achieved security measures and PCI DSS compliance.
Tech: Ruby on Rails, MySQL, Redis, AWS, Payment API Integration
Engineer
Developed and implemented a method to adapt existing mobile sites for smartphones in 1 hour. Achieved user agent detection, responsive design, and touch UI optimization. The tech blog post about this method received over 2,200 Hatena Bookmarks and generated significant industry attention.
Tech: PHP, JavaScript, Mobile Web
Development Leader
Developed a C2C learning service platform from requirements definition. Built from scratch including teacher-student matching, lesson booking, payments, points system, and blog features. Also implemented instructor compensation management and student review systems.
Tech: Ruby on Rails, MySQL, AWS, Payment API
Founder/Developer
Rental server service providing large 1TB storage capacity. Implemented custom file management system, FTP access, and web-based control panel. Achieved long-term stable operation and served numerous users.
Tech: Linux, Apache, MySQL, PHP
Author
Published as OSS a JavaScript library for efficiently displaying emojis as sprite images. Achieved performance optimization and cross-browser compatibility. Published on GitHub and gained numerous stars from the community.
Tech: JavaScript, CSS, Canvas API
Developer
Developed an automated system to collect open data on COVID-19 cases published by prefectures, visualize them as graphs, and automatically post daily updates to Twitter and WordPress. Crawled data every 10 minutes and immediately notified when new cases appeared. Supported multiple prefectures including Kanagawa, achieving over 2 years of continuous operation. Implemented in Ruby with Docker environment. Gained experiential understanding of challenges in open government data.
Tech: Ruby, Docker, Twitter API, WordPress API, Gruff (Graph Library)
Editor / Editor-in-Chief
Served as editor for 3 years and Editor-in-Chief of the 'SFC CNS Guide,' an IT handbook for students at Keio University SFC. Systematically compiled technical information including Campus Network System (CNS) usage, programming, web design, and multimedia production. Led annual revisions to establish it as a widely-used resource from freshmen to advanced students. Oversaw the entire process including editorial team management, writer coordination, layout design, and print distribution.
Tech: Technical Writing, Desktop Publishing, Team Management
08INTERESTS
Practical DIY projects for home renovation and repairs. Leveraging technical expertise to tackle everything from faucet installation to appliance repairs and car mechanics.
Exploring cultures and history around the world. Over 18 years of travel memories documented.
Call Sign: JE1WFV
Enjoying technology and nature through amateur radio. Main activities include APRS, SOTA, and digital simple radio.
Position reporting system combining radio and GPS
Amateur radio operation from mountain summits
Digital radio for business and leisure use