If compared to those typical LN harem story. i say kiss scene is happen a lot but not often like campione level.
Mostly the kiss things in campione are happened in battle and it's necessary for Godou but in Leviathan the kiss are happened in romantic situation.
This MC can handle a girl pretty well. All the girl who kissing him (i'm not sure about Hazumi) if he knows their feeling for him,
he will kiss them back and thanks god there is no something cliche calls "cockblocking" interrupt them.
Luna ask him a kiss and he respond it.
Hazumi the pure girl like angel who got corrupted by Hal
What surpise me is Orihime, as a innocent girl when come to kind of things from early volume, later she is aggressive then i thought.
Asya..well she tried really hard to woo Hal but it always end up fail.(the most pitiful heronie in this series, she got friend-zone hard.)