I like the fact that he can bum a ride midbattle, then swap out to be the active character. Gets him all kinds of places he'd normally take longer to get to (I'm looking at you, Morgan's paralogue).
If you mean personality reasons she's loved him for a long time, and maybe he knew and never acted, maybe he didn't. It's a nice counterpart to the unrequited love Cordelia seems to harbor for him in apparently every support convo series you can send her through (I haven't done much with her yet, waiting for 2nd playthrough on Hard to try using everyone).
Finally...yeah, Sumia Punch. I laughed my arse off at that one.