Night Walker: Mayonaka no Tantei

a 16-color PC-9801 eroge released by Tomboy in December 1993. Nightwalker is an adventure game, focused mostly on character interaction and problem solving. While the main characters of this game have the same names and similar appearances to their anime equivalents, their personalities are generally more easy-going and their backgrounds are less tragic (they all have living relatives). In comparison to the anime, the game is fairly lighthearted, with Shidō and Guni providing comic relief. Nightwalker was initially developed as a spin-off project of the adult game Bishōjo Audition: Find an Idol released by Tomboy in February 1993, with the character Rihoko Ayukawa from that game reappearing as a heroine. However, in the process of refining the setting, the heroine's name was changed to Riho Yamazaki, her design was changed, and the story and setting were separated from the previous work. The concept of the world of Nightwalker itself is based on illustrations from 1992.

Shido Tatsuhiko is not only a private eye…he is also a vampire with no real memory of his past. Joined by Yayoi Matsunaga, a female government agent, Riho Yamazaki, an orphaned teenage girl working as his secretary, and Guni, a little green imp, Shido must face demonic creatures known as Nightbreed. Meanwhile, Cain, the vampire who made him what he is now, is seeking him…