It has its good and bad parts. The good, they would balance each other out and I'd think they'd get along well as sorta "friends". They have a bit of similarities concerning their attitudes and I could see them getting along what with being rebellious and fighters and all (and Buttercup sure likes being a rebel).
The bad...Well, he used her. He knew of her feelings for him and he took advantage of that. And that always sucks. Not to mention the age gap is really creepy. A little bit zaidi and he could've gone to jail for essentially grooming a 5 mwaka old. And of course, there's the thing of him being a villain while she's a heroine.
The pairing could work, but many years later. Once the age gap isn't so wrong and they both mature and develop properly (Ace stops being a villain and Buttercup eventually leaves behind her feelings of hurt pride).
