Kizuku Watanabe is a manga artist and writer recognized for his work on official spin-offs of popular series. Watanabe made his debut in Weekly Shonen Jump in 2010 with Marchen Prince Grimm, a fairy-tale parody manga.

Watanabe is best known as the writer and story planner for Koro Sensei Quest, also known as Koro Teacher Quest, an official spin-off manga of Yusei Matsui's series Assassination Classroom. The series was serialized in Shueisha's Saikyō Jump magazine from October 2, 2015, to October 4, 2019. The manga was illustrated by Jo Aoto, with Watanabe responsible for the story and planning. The complete series was compiled into four or five tankōbon volumes. Koro Sensei Quest reimagines the characters of Assassination Classroom in a fantasy role-playing game setting, featuring the cast as heroes in training tasked with defeating their teacher, who has been cast as a Demon King.

The success of the manga led to multiple anime adaptations. An anime film, produced by Studio Lerche, premiered in Japan on November 19, 2016. This was followed by a twelve-episode original net animation series, also animated by Lerche, which was released from December 23, 2016, to March 9, 2017. The ONA series is a re-cut version of the film. Both adaptations saw the original Japanese and English voice cast from the main Assassination Classroom anime return to reprise their roles.

Watanabe’s work on Koro Sensei Quest involved building a new narrative using existing characters, a task he has described as both complicated and enjoyable. The series is characterized by its comedic tone and chibi art style, focusing on humor and parody while retaining the core dynamics of the original cast.

In 2024, Watanabe returned as the creator of Kaiju No. 8: Relax, a spin-off manga based on the popular series Kaiju No. 8 by Naoya Matsumoto. This continued his role in developing companion works for major shonen franchises.