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Juju-chu!
Yuka Ooka

Yuka Ooka

Background

I’m Yuka Ooka, a software engineer and technical author based in Japan. My React and TypeScript book series, Riakuto!, has sold more than 40,000 copies.

I started out in PHP, working on Infoseek Japan’s front page and member login system, and later on Rakuten’s women’s portal. After that I went independent as a Ruby on Rails developer, moving between clients until one of them, a job service for software engineers, recruited me into a full-time role as their product manager. When I left that company in 2016, I went back to freelancing. React was gathering momentum by then, so I taught it to myself and made it my specialty.

These days I build web applications in React and TypeScript. Lately that has meant the Hono + Inertia + React stack—the same stack that powers this site.

Where These Books Come From

Juju-chu! grew out of Japan’s indie technical book culture. Japan has had a thriving culture of self-published doujinshi for decades, centered on Comiket. Fan-made manga and fiction are the dominant genres, but there have always been a few circles putting out technical books on software and electronics instead.

In 2016, one of the more established circles in that scene took the lead in founding Tech Book Festival (技術書典), held in Tokyo—a Comiket for engineers. It has run roughly twice a year since, and at its pre-pandemic peak it drew more than ten thousand visitors.

What everyone brings to Tech Book Festival is the book they actually wanted to write. So subjects no commercial publisher would take on—technologies too new, too narrow—show up routinely. The covers are just as unconstrained: manga-style illustrations, parodies of major publishers’ house styles, whatever the author feels like.

My first book, Riakuto! (りあクト！), came out at Tech Book Festival 5 in 2018, back when React was still niche in Japan. I was responsible for teaching React at work then, and I shaped those conversations into a book. It landed at the right moment for companies trying to adopt React. Through four revisions keeping pace with React’s evolution, it is estimated to have become the best-selling React book series in Japan.

The Riakuto! series: five volumes with manga-style covers

The Japanese original of Juju-chu! appeared at Tech Book Festival 20 in 2026. Agentic coding had become my normal way of working by then, and managing history had turned into a steady source of frustration—until I ran into a version control system with the strange name Jujutsu and watched the whole pile of problems dissolve at once.

I have to write a book about this, I thought, and wrote it on that impulse.

The characters and dialogue format carry over from Riakuto!. It was the first book on Jujutsu to be published anywhere, and it is, unmistakably, a love letter to Jujutsu.

Current Setup

Most of my day-to-day development happens in the terminal.