Haha that reminds, if anyone is to be Gin's wife, it would be Madao after "that" incident; but I'm off topic. xD
Anyway, same thing with Gin X Tsukuyo I guess applies to Kagura X Okita. Also, as someone above mentioned. Shinpachi has Otsu-chan.
For any of these to change; something very drastic in the setting has to happen.