Character Name: Kamui Shirou Super Power/Mutation: Important person illusion; basically, anyone that looks at Kamui may notice he bears a strong resemblance to whoever happens to be most important to them. This is a skill Fuuma has in canon. He's never shown to bear a resemblance to someone female, but because Kamui is significantly more effeminate he'll be able to look similar to the most important persons that aren't male.
Restrictions: In canon the resemblance never goes away/stops being noticeable unless the person being mimicked dies. If Jack were the most important person to Jill, for example, she would see Jack every time she looked at Fuuma. For Kamui the resemblance will only be brief -- Jill might suddenly notice that Jack and Kamui are similar and maybe even be able to pinpoint why, but in the next moment the resemblance will be gone. And unlike Fuuma, Kamui won't be aware of the resemblance -- making him much more poorly equipped to handle any reactions to it.
Reasoning: This could have been a talent Kamui had in canon, along with several others he didn't get because he chose the side (and indirectly, the set of powers) that he did.