Gekiman! (激マン!) is a fictionalized autobiography by Go Nagai in manga format. It was published Nihon Bungeisha's Weekly Manga Goraku magazine from May 21, 2010 to September 7, 2012, and detailed the creation process of the Devilman manga. It was gathered in 6 tankōbon volumes.
Gekiman! follows the story of Geki Nagai, a fictionalized version of Go Nagai in his days as a manga artist while communicating with other figures including Nagai's real-life editor as well as others such as Ken Ishikawa. Other features included subtle references to Toei Animation as well as Shonen Magazine under pseudonyms that reflect the business side of the franchises' development. A modernized remake of the manga is also shown along with this with updated artwork.
In the Devilman chapter, the process of the creation of the Devilman manga started as a parallel to the manga Harenchi Gakuen. Geki created the world of Devilman while trying to have it reflect the world as best as he could as the use of widely known news was not available through mediums like mobile phone use in the modern age. To this end, Geki tried to implement elements such as Soviet Russia and its weapons but was told by his editor to leave them subtle but contemporary. Events that the manga reflected included the Gulf War and the sarin attack on the Tokyo subway (comparing it to the Jinmen event) that were decades before their time. Some elements while already controversial in the then more controlled Weekly Shonen Magazine had to be removed including a highly gruesome death and a rape scene during the fight with Sirene. The final chapter mentions that the decision of a handsome young man as the hero was by the editorial department which was stated to be part of the reason that fans were able to follow the story for so long. However because of this, Geki created the related character of Violence Jack as a more literal personification of a 'Devil Man' as a metaphor that the story of Devilman was completed.
The Mazinger chapter tells a different story of Geki Nagai having a different appearance and personality. However as revealed in one chapter, because of Mazinger and Devilman's publications both iterations had to switch around to meet deadlines in their respective magazines. It also reveals how the different franchises blend in and influence each other. The Cutey Honey chapter features a female Geki named Kageki with mostly gender flipped characters as she tries to break in a new series that strays from previous works.
- On Jul 4, 2014 a sequel started, titled Gekiman! Mazinger Z no Shou (激マン！～マジンガーZの章～, "Geki-man! ~The Mazinger Z Chapter~") covering the creation of the Mazinger Z franchise. With that arc's end on July 29, 2016, another chapter called Gekiman! Cutey Honey Shou (激マン! キューティーハニー編, "Geki-man! Cutey Honey Chapter").
- The removed Sirene rape scene was eventually used and adapted in Devilman Crybaby.