Was expecting they will find a wig and maybe a dress in her room, but it was being cleaned so she had to take it with her, but spraying the floor with those chemicals in order to reveal she entered Bertia room was surprising twist.
Cecil is clearly evil, there's no denying it, but maybe Bertia and Heronia playing the game passed it normally and it always was Bertia turning Cecil into Demon Lord while Heronia "drug magic" caused him to become passive/in love, but there was a hidden route both didn't get to play, which is pretty common in good games.
Thanks for the scanlation!