Kazushi Hagiwara was born on April 4, 1963, in the Nakano ward of Tokyo, Japan. He is a manga artist and original creator best known for the long-running series Bastard!!. Before his debut, Hagiwara worked as an assistant to hentai manga artist Dirty Matsumoto and later assisted Izumi Matsumoto on the production of the romantic comedy manga Kimagure Orange Road. He is a high school dropout but later graduated from Tokyo Designer Gakuin College. Hagiwara made his debut in Weekly Shonen Jump with two short stories, Binetsu Rouge in 1987 and Virgin Tyrant in 1988.

Hagiwara is most famous for creating Bastard!! (full title Bastard!! Heavy Metal, Dark Fantasy), which began serialization in Weekly Shonen Jump in 1988. The manga is noted for its high level of violence, fantasy imagery, and frequent references to heavy metal music, with character names and locations often derived from band names and song titles. He also cites Dungeons & Dragons as a major influence on his work. The series became popular for its detailed, high-quality artwork that made extensive use of mechanical tones. However, Hagiwara also gained a reputation for his perfectionism and slow production schedule. The manga moved from Weekly Shonen Jump to the quarterly Shonen Jump Special Edition, then back to Weekly Shonen Jump with a monthly schedule, and eventually to the monthly magazine Ultra Jump, where it has been published irregularly. The manga has been on an extended hiatus since 2010. Despite its irregular publication, the series has over 30 million copies in circulation.

Beyond the manga, Bastard!! has been adapted into anime several times. The user query references Bastard!! Ankoku no Hakaishin: Jigoku no Chinkonka-hen, which is part of the original six-episode Bastard!! original video animation series released in the early 1990s. A new adaptation, titled Bastard!! -Heavy Metal, Dark Fantasy-, was released by Netflix in 2022, covering a portion of the manga's story.

Hagiwara's work on original anime projects includes Combustible Campus Guardress (Bakuen Campus Guardress), a four-episode original video animation released in 1994. While the project was created by Satoru Akahori, Hagiwara is credited with the original character designs for the series. His artistic influence extends to video games as well. In 2012, he designed the armor for the Geomancer and Rune Fencer jobs in the Seekers of Adoulin expansion pack for Final Fantasy XI, released in 2013. He also provided character designs for the television anime Endride in 2016.

Hagiwara is also active as a doujinshi (self-published) artist. His group of assistants is called Studio Loud In School, and they regularly publish the doujinshi Wonderful Megadeth, as well as works featuring characters from fighting games like Dead or Alive and Virtua Fighter. He is considered a significant figure in manga, known for his detailed art style and for influencing the visual presentation of fantasy manga from the late 1980s and early 1990s.