It's not been terribly often that they talk of family, not in any kind of detail. It's a touchy subject, especially when it comes to Mom, and the older Kirk has a far rockier relationship with her than the younger does. He's already all but wincing at the idea of dropping the Nexus knowledge bomb on her, let alone taking her to an entirely different universe to watch her son get married, and is opening his mouth to express his condolences for being stuck in that kind of corner.

And then he asks that question.

It's so far from what Jim was expecting that he's momentarily thrown for a loop, eyes widening in surprise. He hasn't thought of himself as a brother since Sam left, but... that is what they are here, isn't it? Close enough, at least, and not just because their genetics are presumably identical enough to bypass each other's biolocks. If there are secrets that Jim can entrust to no one else, he knows he can share them with his companion, that he will understand even if no one else will. What is that, if not brothers?

He's still reeling a little from that, but there's also genuine interest in the way he leans forward a little, a flattered sort of smile teasing at his lips. "Wow, that's really... I'd be honored. How would that work, exactly?"