Kira doesn't know Leon so well, so he doesn't really have a personal sense of him. He seems to be a competent and even-handed commanding officer, which is a nice change of pace for once, so Kira really won't question anything until Leon starts showing a reason why there could be problems.

Professionally, Nanoha trusts Leon. He's intelligent, he's quick-thinking, and he knows how to delegate and let the respective departments do their jobs without trying to micromanage things he has little experience with. She supports him as Captain very firmly and was rather pleased that he ended up getting elected, and hopes to not let him down with her work.

Personally, she almost finds his stone-faced serious personality endearing, really. Not everyone can be as cheerful as she is, and she knows that, and she doesn't have a problem with it (though it wouldn't kill him to crack a smile once in a while, would it?). There's probably a part of her that looks up to him a bit because he does always seem to have things under control and he's a bit more experienced than she is.

As a fellow parent, she can relate to him (she's the strict one, too!) and would really like to spend more time getting to know his family and Sherry.