Okay so, dunno if you guys are okay with me jumping in like this but... I had an idea I'd like to share, working off my previous one. What if said evil magical girl was an older one (not Rita Repulsa old here but like... late 20s) and has discovered her powers dwindling. What if she got in in her head that if she could collect enough sexual energy from younger magical girls, she could restore her own powers.
Also, what if said evil magical girl had 2 - 3 other magical girl's (I dunno, maybe traitors) working for her, in promise that they gain the knowledge that their boss hopes to invoke?
I dunno. Just an idea.