JPEN

BOOKS

Books

“#100 Day Challenge” (Nikkei BP, two translations), the unfiltered edition on BOOTH, and “コードを書かない Claude Code” on Amazon.

Cover of #100 Day Challenge (with obi)

Nikkei BPAmazon No. 1Reprinted

“#100 Day Challenge: I Built an App Every Day for 100 Days and It Changed My Life”

Nikkei BP ／ Published January 11, 2025

A5, 224 pages, 1,980 yen (tax included), ISBN 978-4-296-07106-7 (Japanese)

The record of building a piece of software every day from October 28, 2023 to February 4, 2024 and posting it on X. Reached No. 1 in Amazon Japan's programming category and went into reprint. Korean and Traditional Chinese editions are out.

Amazon (Japan)Korean edition (Kyobo)Traditional Chinese edition (books.com.tw)The day it came out

Cover of #100 Day Challenge: The Unfiltered Edition

BOOTHDigital

“#100 Day Challenge: The Unfiltered Edition”

BOOTH (digital) ／ Released July 15, 2026

Digital edition, 1,480 yen (Japanese)

Everything that did not fit in the Nikkei BP book, expanded into a separate one. The kind of stories a commercial book has no place for.

BOOTHThe day it came out

Cover of コードを書かない Claude Code

AmazonPaperback & Kindle16 chapters

“コードを書かない Claude Code” (Claude Code Without Writing Code)

Hundreds LLC ／ Published September 5, 2026

Paperback and Kindle, A5, 203 pages, 16 chapters plus appendices (Japanese), ISBN 979-8170810857

A year of handing Claude Code the everyday work of a one-person company: preparing documents, placing orders with contractors, revising documents delivered to clients, social media, and deciding which commissioned jobs to take. The text contains no programming. The appendix sorts 41 things that went wrong into six patterns.

Amazon (Japan, paperback)Amazon (Japan, Kindle)The day it came out