AI Product Engineering Studio

From idea to a
working product.

From shaping the requirements to running it in production. / The person who designs it is the person who builds it. / A former hotel manager, thinking from how the floor actually runs.

AI agents, internal systems, SaaS. Shingo Kumon takes it from shaping the requirements through design, build and production, as one person.

  • www.hanaminail.com
    The Hanami Nail style feature page “Sakura”, showing hand-painted cherry blossom nail designs
    Hanami NailAs of Oct 2026
  • www.sharenail.com
    The SHARENAIL comparison table, placing hourly chair rental next to monthly rental, a home salon, and contract work
    SHARENAILAs of Oct 2026 · Halloween
www.hanaminail.comAs of Oct 2026
The Hanami Nail style feature page “Sakura”, showing hand-painted cherry blossom nail designs
www.sharenail.comAs of Oct 2026 · Halloween
The SHARENAIL comparison table, placing hourly chair rental next to monthly rental, a home salon, and contract work
shingokumon.com — CI (replay)
Lint clean, no type errors, 117 tests passing, 79 static pages generated. This is a replay of a verification run from 2026-10-17; no commands are being executed in your browser.
Shipped Systems

Not concepts.
Systems in production.

The screens below are photographs of live sites, taken as they are. They are not mockups, and they are not generated images.

LINE × AI SaaS

MUSUBU

LINE × AI booking system for beauty salons

Before
Bookings and enquiries were tied to opening hours and whoever was free to answer. A message at midnight, or one in another language, sat untouched until the next morning.
Built
An AI assistant inside the salon’s LINE Official Account that carries an enquiry through to a confirmed booking. Confirmations and changes are handled from a dashboard that works on a phone.
  • → Booking completed without leaving LINE
  • → Enquiries answered around the clock, in several languages
  • → No commission per booking
  • LINE Messaging API
  • Claude API
  • RAG
  • Supabase
  • Next.js
Visit MUSUBU
musubu-lp.vercel.appAs of Oct 2026
The MUSUBU booking dashboard, showing bookings by date, revenue, and alerts for open slots
A LINE conversation picking a date and time, through to a confirmed booking
Inbound Platform

Hanami Nail

Beauty discovery platform for visitors to Japan

Before
There was no route, in English alone, from a visitor arriving in Japan to a salon here.
Built
An English content platform with a structure that lets categories go live one at a time.
  • → English content
  • → Category-based publishing structure
  • Next.js App Router
  • Supabase
  • Vercel
  • Multilingual
Visit Hanami Nail
www.hanaminail.comAs of Oct 2026
The Hanami Nail style feature page “Sakura”, showing hand-painted cherry blossom nail designs
Matching Platform

SHARENAIL

Chair-rental matching platform for nail artists

Before
The operator could not see where each applicant stood — from sign-up through a viewing, the contract, and going live.
Built
Sign-up, screening, viewing, contract and go-live arranged into a single path, with the operator in the loop. Includes the admin dashboard and the email that goes out automatically from the confirmed date (idempotent, sent each morning).
  • → Registration-to-go-live workflow
  • → Admin dashboard and automated email
  • Next.js App Router
  • Supabase
  • Admin dashboard
  • Auth
  • Scheduled email
Visit SHARENAIL
www.sharenail.comAs of Oct 2026
The SHARENAIL comparison table, placing hourly chair rental next to monthly rental, a home salon, and contract work
What I Build

Four things
you can hand over.

I start from where your time is going, not from the technology. If a feature will not earn its place, I will say so rather than build it.

01

AI systems and agents

AI that answers from your own documents and data, LINE conversations that run through to a confirmed booking, and the operational design that keeps generation running in production. I decide where a request gets handed back to a person before building anything, because accuracy will not always be there.

02

Web apps and SaaS

Auth, roles, admin dashboards, notifications, payments. The product your business runs on, designed and built as one piece.

03

Workflow automation and integrations

Scheduled jobs, automated email, and integrations with LINE, social platforms and payments. Less copying between systems, less checking by hand.

04

Changes to systems already running

Changes and speed work on what you already have, plus operation and incident response after launch. Ongoing maintenance is from ¥30,000/mo.

Technology Stack

Only what runs
in production.

Nothing here is on the list because I tried it once. Every item is running in a product that is live today.

Frontend
  • Next.js (App Router)
  • React
  • TypeScript
  • Tailwind CSS
  • Responsive and performance work
Backend
  • Supabase / PostgreSQL
  • Row Level Security
  • Auth and permission design
  • Route Handlers / webhooks
  • Schema design and migrations
Infrastructure
  • Vercel
  • GitHub Actions
  • Cron jobs
  • Resend (transactional email)
  • First response on production incidents
AI
  • Claude API
  • RAG over your own data
  • Prompt design
  • Running LLM generation in production
Integrations
  • LINE Messaging API
  • Payments
  • OAuth and third-party APIs
  • Social APIs (Threads / X)
Two Ways to Work

Have it built,
or have me on the team.

Project work delivered as a product, or a contract engagement billed by the days I work. Either one is fine.

A — Build it for you

Have it built

A system built from scratch, AI brought into what you already run, or a one-off piece of work. You do not need a finished spec. I look at how the work runs today and quote from where the return is clearest.

  • Start smallSMALL · 2–4 weeks¥300,000 – ¥600,000
  • Systems for daily operationsSTANDARD · 1–3 months¥600,000 – ¥1,500,000
  • A product your business runs onPLATFORM · 3+ monthsfrom ¥1,500,000
  • Maintenance & operationsUpdates, backups and incident response after launchfrom ¥30,000/mo
B — Join your team

Bring me onto the team

Open from January 2027

My time is currently taken up by the products I run. From January 2027 I can take on new work, starting at around two days a week. A conversation now about a later start is completely fine.

  • 1 day / week8 hours per weekfrom ¥200,000 / mo
  • 2 days / week16 hours per weekfrom ¥400,000 / mo
  • 3+ days / week24+ hours per weekfrom ¥550,000 / mo
  • One-off sessionTechnical direction, architecture review, a look at existing code¥50,000 / 90 min
Contract
Independent contractor, renewed monthly
Location
Fully remote. I do not work on-site
Hours
Calls during Japan business hours (JST). Async work otherwise
NDA
Happy to sign yours
Development Process

The same route,
every time.

The work does not change hands halfway through. The person you first talk to is the person who carries it to the end.

  1. 01

    Talk

    Tell me what you need. The spec does not have to be settled.

  2. 02

    Requirements

    Shaping requirements and deciding what comes first

  3. 03

    Design

    Database design

  4. 04

    Build

    Implementation, both frontend and backend

  5. 05

    Review

    Code review, Deployment and CI

  6. 06

    Operate

    Running it after launch, including incidents

Start a Project

Tell me what is
in your way.

You do not need a finished spec. We can start by working out which part is worth automating first.

Send it any time. I reply within 1 business day.
Availability and monthly rates for contract work are on /en/work; pricing and how a project runs are on /en/services.
By email: info@shingokumon.com.