Er, it's more like...the character in question finds the female characters "cute" so Kamui gives her a potion that is supposed to fix it...which it does, and apparently she ends up liking Kamui instead.
Actually, that's not any better.
Yeah, imma skip out on FE: Fates.
That wasn't what happened. The character in question, Soleil, finds girls very cute to the point where she sometimes is too shy herself to talk to them and when she does try to speak with them, she ends up fainting or something similarly. Just basically, she loves girls, but has problems talking to them. Kamui finds it strange, but decides to help her with her problem. He places some powder in her drink(regardless of good intentions, I don't find this acceptable.) that alters her vision into making all guys look like girls, including Kamui. Kamui then tries talking with her while Soleil sees him as a girl to help overcome her shyness to girls. IIRC, this doesn't help fully and Kamui apologizes for it not fully helping her with her shyness, but Soleil thanks him for trying. But as mentioned, in their S-support, she mentions she's fallen for him because of seeing him as a girl and whatnot and even Kamui is weirded out.
Basically, that's the gist of it. It wasn't Kamui trying to fix her attraction to girls like idiots were proclaiming. It was him trying to help her overcome her problems with talking to girls. Really, the supports weren't as terrible as people were proclaiming. Sure, there's parts of it that I don't approve, like placing the powder in her drink without her knowledge, but at the same time, it had it's moments, cause while Soleil has the effects of the powder on her, before leaving, she proclaims she wants to see what the boys in their army look like as girls(would've loved to see her reaction to "Female Foleo").
Now, note that I'm not trying to do any convincing here. If you don't want Fates, that is fine. I'm just resolving the Soleil/Kamui issue and that the actual Supports between them aren't as bad as people were making them out to be and how there was alot of misinformation that was spread.