About / @reizist

Reiji Kainuma.

Career, skills and selected experience as a software engineer in Tokyo.

Updated · Wed Apr 15 2026 00:00:00 GMT+0000 (Coordinated Universal Time) Download PDF
73 Overall Score

Findy Numbers are skill deviation scores calculated by Findy based on open data from GitHub accounts.

Language Scores

  • Python
    73
  • Ruby
    65
  • JavaScript
    63
  • TypeScript
    59
  • PHP
    58
  • Go
    49
  • C
    47
  • Java
    45

Tech Stack

  • Ruby on Rails
  • Ruby
  • Python3
  • FastAPI
  • Fluentd
  • BigQuery
  • Presto
  • AWS
  • Google Cloud
  • Docker

Engineering Roles

  • Backend Engineer 10+ yrs
  • DevOps Engineer 5–10 yrs
  • AI / LLM Engineer ~1 yrs

Management

  • Tech Lead 1–2 yrs
  • Product Manager 1–2 yrs
  • Project Manager 1–2 yrs

Profile

Reiji Kainuma
Age
36
Location
Kanagawa, Japan
Employer
Fez, inc

Recent Development Experience

  • New development and operation of a BI service using Next.js / FastAPI / LangChain / Google Cloud
  • Redefining the data analysis process in the generative AI era (automating generative AI from a Semantic Layer, automating marketing analytics)
  • Contribution across the marketing automation flow (target planning → market analysis → target extraction → quantitative review)
  • Data development using generative AI (extracting new product axes and analyzing user preference trends using vector data)

What I Want to Do Going Forward

  • I want to grow products by performing fact-based policy review / planning using generative AI and data.
  • I want to join a finance- or real-estate–focused startup and redefine products for the generative AI era.

English Proficiency

Level
Basic conversational level

Work Experience

  1. 01 2023.04 — Present 3y 1m

    Fez, Inc. Full-time Employee

    Urumo BI

    2023.10 — Present
    Position
    Full-stack Engineer
    Management Role
    Tech Lead
    Team Size
    10–50 people
    Role
    Manager
    Technologies
    • Google Cloud
    • BigQuery
    • Looker
    • FastAPI
    • ChatGPT
    • LangChain
    • Claude

    After the launch phase of Urumo BI — a BI service that contributes to sales lift through data analysis using brick-and-mortar store purchase data (ID-POS) — I organized the team and now manage daily operations across the PM team, development team, and data team. We provide functions that perform data analysis (product analysis / customer analysis) and marketing use cases (customer extraction) for retailers and manufacturers, monitoring daily usage status and gathering enhancement / feature requests. As the title "Product Engineer" suggests, I handled prototyping for 0-to-1 development myself, contributing to front-end, back-end, and infrastructure. Currently, the management-persona aspects have grown, so I have stepped back slightly from hands-on implementation. However, I continue to catch up on my own, e.g., building a corporate site with generative AI using Claude Code to boost productivity.

  2. 02 2020.04 — 2023.03 2y 11m

    Quipper, Inc. Full-time Employee

    Building the Data Platform for Studysapuri / Studysapuri English

    2020.04 — 2023.03
    Position
    DevOps Engineer
    Team Size
    1–10 people
    Role
    Team Lead
    Technologies
    • Docker
    • Google Cloud
    • BigQuery
    • Terraform
    • Python3
    • Embulk

    Built a new data platform on top of BigQuery using Airflow (Cloud Composer) and Embulk.

  3. 03 2019.03 — 2020.03 1y

    Quipper, Inc. Full-time Employee

    Development of an English-Training Feature for Studysapuri

    2019.03 — 2020.03
    Position
    Backend Engineer
    Team Size
    10–50 people
    Role
    Member
    Technologies
    • Ruby
    • Ruby on Rails
    • React
    • Terraform

    Joined Quipper's web dev team, contributing to a year-long large-scale development project — performing Rails upgrades, restructuring logs, and developing audio-training features.

  4. 04 2018.02 — 2019.03 1y 1m

    Recruit Marketing Partners Co., Ltd. Full-time Employee

    Development and Operation of "kidsly" — A Business Support System for Nursery Teachers / Nursery Schools

    2018.02 — 2019.03
    Position
    Infrastructure Engineer
    Team Size
    10–50 people
    Role
    Member
    Technologies
    • Ruby
    • AWS
    • Ruby on Rails
    • Fluentd
    • Terraform
    • CircleCI

    Operations and development of a web application using Rails / building a log infrastructure using fluentd / building a secure image-delivery environment using CloudFront / refactoring of the infrastructure-management environment via Terraform (modularization, workspace removal, code-ification of Lambdas via Apex).

  5. 05 2017.02 — 2018.01 11m

    Repro Full-time Employee

    Development, Operation, and Monitoring of the Backend for a Marketing Automation Tool

    2017.02 — 2018.01
    Position
    Infrastructure Engineer
    Team Size
    10–50 people
    Role
    Member
    Technologies
    • Ruby
    • AWS
    • Docker
    • Fluentd
    • Terraform
    • Presto
    • Datadog

    Operation and development of a fluentd cluster / operation of the distributed datastore Presto and construction of its monitoring environment / construction of a monitoring environment using Datadog and OSS development.

  6. 06 2014.04 — 2016.12 2y 8m

    Ignis, Ltd. Full-time Employee

    Operation and Development of the Social Game "Bokudora"

    2014.04 — 2016.12
    Position
    Backend Engineer
    Role
    Member
    Technologies
    • Ruby
    • MySQL
    • AWS
    • Redis
    • Ruby on Rails
    • AWS CloudFormation

    Development and operation of a social game / management and localization of the overseas (Taiwan) rollout.

Education

  • The University of Electro-Communications March 2013
    Department of Computer ScienceGraduated

Self-PR

bot → @reizist-bot

AI Utilization in the Engineering Domain

Continuously updated based on talks and internal case studies. https://speakerdeck.com/fez_dev/fez-cloud-next-tokyo2024-hureikuautosetusiyond1-da-07