Sephiria 1.0 includes a range of costumes that are either available immediately or unlocked by meeting specific in-game challenges. The guide matters to players seeking to customise their character, as several costumes require focused runs, repeated enemy defeats or random events.

Unlockable outfits include Red-Clothed Cat and Frog for reaching 50 Fire or Lightning damage respectively, while White Wolf requires defeating Pillager Leader Rataka more than five times. Secret costumes involve taking 333 total damage in one dungeon run, completing five random Blood Donation events, or owning the Steam game Dungreed; eight rabbit-themed costumes are available by default. A further seven costumes have been added, but their unlock requirements were not yet known.