secret character; hidden character
Video game term for a playable character that is not initially available and must be unlocked or discovered.
There are three secret characters in this game.
You need to meet certain conditions to unlock the hidden character.
Compound of 隠れ (kakure, 'hiding') + キャラ (kyara, clipping of キャラクター 'character'). The exact origin is uncertain, but it likely arose in gaming communities.