Random thought, on reading it:
It might be slightly better phrased if 'giving over' were treated something like reading the situation. You'd say what your instincts suggest you should do, roll+weird, and on a hit you have bonuses for if you follow that course of action. It'd be almost identical in function (I think?), but I think it'd be clearer how it applies.
Though, it also seems to me like it would make good sense to move the decision into MC hands: the MC says what your blood urges you to do. After all, we seem to be talking about an external influence here ... it's about your heritage and your blood, and how that might overrule what you think to be your personal beliefs and desires, right?
The MC would want to ask questions to determine the nature of your blood, of course, much like he asks questions to determine how you interact with the maelstrom.
Also, why are the urgings of your blood more-or-less combat-oriented? The acting under fire option opens thing up a bit, but it seems like you could easily, say, have a dude who's blood urges him to pander and seduce. It'd be more broadly applicable to just have 1 hold turn into +1forward, but you had to have deliberately chosen otherwise, I'm thinking.
Is it that the pander/seduce guys actually just have weak blood, and blood is in direct opposition to being all treacherous (read: civilized)?