I was actually thinking about it....but the man doesn't do anything unless he has to/someone forces him to. But maybe, I'll stick something in next Monday's plotting meme thinger. He really does need something to do.
That...is actually a really good question. There's a ridiculous amount of fanfic out there detailing all the lovely things those two could have gotten up to. One of the things mentioned was Fai getting Kurogane to teach him some Japanese, which I can actually see happening. Otherwise, he probably just attempted to do TRC-version sign language and tried to persuade the other soldiers that Kuro was his husband some weird serial killer/gay/a doting father/some other thing the ninja would not approve of. Watch Kurogane practice/train peole and make suggestive comments on the side no one understands. Possibly keep a journal. I get the feeling he spent a lot of time on his own, but I'm not exactly sure what he was doing with all that free time. Emo in a corner when no one was looking?
Anyway, no more tl'dr.
Fuuma's wish! What is it? (You've probably answered this elsewhere, but I'm too lazy to go find it.)