Spoiler tagging for anyone reading this that would prefer to avoid them:
The ending where all the girls end up being converted into succubi is the main "evil" ending where the player sides with Mira. There's one where Cerise happens to get caught down the main route and Mira ends up succeeding without the players help, which is arguably a more evil ending. This walkthrough highlights the Cerise captured route in purple. Hope this helps but always glad to answer more questions!