01
Vision
Design the growth of people, business, and culture.
Shimpei Oshima (SHIN)
Indie Developer / Solopreneur
I'm an indie developer building Shopify apps for stores in Japan on my own, working alongside AI coding tools. Planning, design, development, app review and customer support are all handled by one person.
I started as a book editor (two companies), moved into engineering (five companies), and built a platform service with more than five million users and a global manufacturer's e-commerce site. I founded Pepin in January 2026 and went full-time that March. Shopify apps and commerce support are the core of the business, alongside COSMA, a marketplace for cosplay.
What I build
Four Shopify apps and one web service, each built and run by one person.
- 01
In-store appointment and event booking calendar, staff and resource management, customer records with visit history, and adding bookings to Google Calendar.Shopify booking appLaunched Mar 2026Shopify booking appLaunched Mar 2026
Maru Booking - 02
Site search that handles Japanese spelling variants, searching products, blog posts and pages, SKUs, and search analytics.Shopify search appLaunched Apr 2026Shopify search appLaunched Apr 2026
Maru Search - 03
Estimates, plus invoices, delivery notes and receipts under Japan's invoice rules, with CSV export for accounting and shipping.Shopify invoice appLaunched Apr 2026Shopify invoice appLaunched Apr 2026
Maru Invoice - 04
Best-seller rankings published automatically, with attribution and A/B testing.Shopify ranking appLaunched Apr 2026Shopify ranking appLaunched Apr 2026
Maru Sales Ranking - 05
A marketplace dedicated to cosplay, for buying and selling costumes, wigs and props.Web serviceWeb service
COSMA
Career
- 2012
Started out as a writer and book editor, covering interviews, writing and editing.
- 2016
Switched to web engineering, working as a front-end engineer on in-house services and e-commerce sites.
- 2019
Moved to Fukuoka and rebuilt a web service's owned media and e-commerce site, which began a long involvement with Shopify.
- 2022
Joined a global manufacturer as its only in-house engineer, building and improving its Shopify store.
- 2026.01
Founded Pepin.
- 2026.03
Left employment to work on Pepin full-time, building the Maru series of Shopify apps alone and releasing them on the App Store.
What I write about
Notes on what I tried and where I stumbled while building a business on my own.
- Building a Japanese Search Engine in Rust, on My Own
- Building Shopify Apps Solo with AI — What I Delegate and What I Keep
- Strategy to Reach 100 Installs for a Shopify App: A Solo Developer's Realistic Plan
- Shopify App Submission to Launch in 30 Days: The Full Journey Log of Maru Booking
- Three Months of Shopify App Store Rejections — A Solopreneur Submission Diary
- What Shopify Merchants Actually Wanted from a Booking App — A Solopreneur Founder Note
I also talk about it on video
On my YouTube channel, SHIN | 1人で事業をつくるソロプレナー, I talk about working independently, money, and the reality of indie development (in Japanese).
02
Mission
Build products that make people and businesses better.
03
Philosophy
Small improvements. Long-term impact.
Business Information
- Business Name
- Pepin
- Established
- January 5, 2026
- Address
- 〒150-0021 Ebisu, Shibuya-ku, Tokyo
- Owner
- Shimpei Oshima
Start by telling us what is stuck.
App questions and broader Shopify questions are equally welcome. Nothing needs to be fully specified yet. We usually reply within two business days.