The adult visual novel publisher was first established on February 24, 1993, and will celebrate its 30th anniversary on February 24, 2023.
The teaser website features a countdown that ends on March 31 at 9:00 p.m. PT / April 1 at 12:00 a.m. ET / 14:00 JST, on top of a visual illustrated by Itaru Hinoue—which appears to show Mizuka Nagamori from ONE: Kagayaku Kisetsu e.
ONE: Kagayaku Kisetsu e was originally released for PC on May 29, 1998 and features artwork by Hinoue. A PlayStation port was released on April 1, 1999. Said port was also what led Fate series writer Kinoko Nasu to get into writing games (thanks, Frontline).
Watch the teaser trailer below.