The idea of victini attacking the MC is a good idea and she could have a personality of being #1 so she heard he was beating legends and wanted to stay at the top in a 1VS1 fight that cant be won if he waits for her to tire so he would need change tactics by using his moves to stimulate her heat. Ex: His swift move can have him slap her butt since she is psychic is effective until she wants to lose and have sex instead. She could gloat to the other legends of that region that she was caught first before them and have more kids than the other legends.
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Her always wanting to be #1 makes sense, I can see that turning into her cheering everyone else for being #1 once she's been caught, just obsessing over victory of any kind whether it's hers or not!
Teasing and arousing her through the fight is a good plan, I think I've got enough ideas for her now, I can note them all down and be ready when I get to Chapter 5