Pre-orders will include Go-Home Club costumes, and costumes that will allow you to more easily progress through the game. There are no plans to release these as downloadable content at a later date.
The 12 swimsuit costumes released for the PlayStation 4 version, which launched in Japan in May, are all included in the base game.
The Caligula Effect: Overdose recently dated for release across PlayStation 4, Switch, and PC in North America on March 12, 2019 and Europe on March 15, 2019. In Southeast Asia, an English version is already available for PlayStation 4.