What is a character?

Characters are playable chars inside Mugen, the game. You can add or remove them to your game.
Theoretically, It is possible to add all the characters you want because the number of blocks or spaces to add new ones is editable.

Here in HCM, Characters are categorized in 2 kinds: Rapists - Aggressors and Victims.

Rapists and Victims?

Yes, Characters are categorized inside those 2 main groups.

Rapists or Aggressors: Characters created with special attacks to rape the opponent or just attack ferociously.
Victims: Characters created with special attacks and erotic moves, commonly sexy characters (guys or girls), basically the victim who will be raped or assaulted.