He started his professional career at Shogakukan in 1980 and worked as an editor on the publisher's various manga magazines, including as editor-in-chief of Big Comic Spirits from July 1999 to 2001.
Since becoming freelance, Nagasaki has worked as an author under various pen names, such as Keishi Edogawa (江戸川啓視), Garaku Toshusai (東周斎雅楽), Big O (ビッグ・オー) and Richard Woo (リチャード・ウー).
"[1] Brian Ruh of Anime News Network described Nagasaki as the only editor who "has risen to the level of co-creator alongside the artist.
[19] In 2016, the manga was adapted into a 10-episode TV drama and a theatrical film, and the duo created a short sequel arc subtitled 999-hen.
[23] That same year, Nagasaki teamed up with Seimu Yoshizaki for the female detective manga Deka Girl, which ran in Kodansha's Kiss Plus until August 2011.
[25] Nagasaki wrote the historical novel Arutantahā Tōhō Kenmonroku Kitan for Kodansha's Pandora Vol.2 Side-B magazine,[26] before it was published as a standalone book in 2010.
[28] To celebrate the 90th anniversary of Shogakukan, Nagasaki produced a 2011 picture book adaptation of Kosuke Hamada's story Red Oni Cries that was illustrated by Urasawa.
[29] In April 2012, Shinchosha published the first novel in what would become Nagasaki's Daigo Shinji no Hakuran Suiri Files franchise that follows a manga editor who solves mysteries.
[32] Nagasaki reunited with Yoshizaki to create the science fiction detective series Usagi Tantei Monogatari (2012–2013) for Kodansha's Kiss.
[33] At the end of 2012, Nagasaki started working with Michitsune Nakajima on Yamaterasu Code, which was serialized in Shueisha's Jump X until the magazine was cancelled in 2014.
[34][35] As Richard Woo, he and Yoshizaki created Abracadabra: Ryōki Hanzai Tokusōshitsu in Big Comic Original Zōkan from 2014 to 2020.
[14] In 2018, Richard Woo began Himiko -Shinsetsu Yamataikoku-den-, about the ancient queen of the same name, with Mariko Nakamura in Big Comic Original.
[39] Richard Woo created M no Shirushi -MacArthur Ansatsu Keikaku- in 2020 alongside Ryoichi Ikegami for Shogakukan's Big Comic Superior.
It was adapted into a manga for Monthly Big Comic Spirits by Akira Iwaya in March, and Nagasaki wrote a novelization published in May.
[45] Richard Woo and Yoshizaki began the suspense manga Minzoku Gakusha Akasaka Yaichirō no Jiken-bo in the October 2022 issue of Kodansha's Monthly Afternoon, which was released on August 24, 2022.
In addition to finding it faster to just write the story himself from the get-go, Nagasaki began to enjoy it the more he did it, until finally deciding to switch jobs from editor to manga author because he felt it would be more interesting.