Depends on the diffinition of tame.
In my story, {yeah, it's back to that story again,} one of my characters is a vampiress. Yeah, i know, not human, but please, bear with me. When we're first intoduced to her, she's very... uptight. Most vampires have a form they can slip into if things get hairy...
(PUN... number 1.
)
... but she belongs to this other group of vampires that are all about... purity. Not good purity, more like, keeping things within one own's species.
(PUN... number 2, and where's the fun in that?)
She meets a werewolf, and they fall in love. He takes her out on a run one night, and she picks a wolf as that other form.
Significance? Big time. THe animal she picked represented her disision to stay with him. By the end of the story, she's not as uptight, and, in fact, is actually... feral i'd say? Starting off, the werewolf's... basically living his life for once. He didn't expect to find her, or to fall in love with her. He did, and he became, sligtly less wild.
Okay, long boring story short, they allowed the other to change, so that they could be together. Now, if your characters really love each other, it shouldn't matter if he's a werewolf, or a were cheetah, mongoose...
(... MONGOOSE? What the heck?)
It's an idea... or, if he was a blue and purple spotted wolf with three legs, two heads, and no arms.
({blink} that's scary.
But other than that, yeah. Your werewolf will probably find out it was more of a hassle keeping it secret than just telling her. Ain't it usually that way?)
Usually... the sister is a kitsune? Hmmm... that's... wait, is she adopted or something?
Plus, the only other major question is, can he control himself in that transformed state? If he can't, or... hey, is this the first time he's had a long term relationship?
P.S. I'm starting to read the Twilight series myself. Sounds interesting...