| Console: | Sega Dreamcast |
| TV Standard: | NTSC-J |
| Country: | Japan |
| Developer(s): | Princess Soft |
| Publisher(s): | Princess Soft |
| Release Date: | 2001-12-27 |
| Players: | 1 |
| Co-op: | No |
| ESRB: | E - Everyone |
| Type: | Adventure |
21: Two One is a Japanese murder mystery visual novel developed by BasiL, it was first released as an adult PC game for Microsoft Windows on May 25, 2001. 21: Two One was later released for the Dreamcast by PrincessSoft on December 27, 2001. The game is the second installment by BasiL, and after the completion of 21: Two One, BasiL went on to create their third and final eroge, Cherry Petals Fall Like Teardrops, before forming a new company called Navel. The story follows a young man called Takuya Kirishima, who is a talented surgeon and works in a hospital with his childhood friend Seri Sakaki, however, one day a murder is committed at the hospital, and Takuya tries to solve the mystery. Gameplay in 21: Two One offers branching plot lines, and a multi-choice navigation, where the player can attain multiple endings.
