Niwa and Kaoru interaction is the best (though that is also not a pairing of mine.. *with my Kaoru going.. 'that big lug is not a suitable companion for me.."* He'd much rather have a certain 'knight.
You know if you think about it. Kaoru = Guienevere, Niwa = King Arthur, Omi = Lancelot and Nakajima = Merlin.
That way you get Niwa/Nakajima (Merlin/Arthur) and Omi/Kaoru (Guienevere/Lancelot). It really reeks of authurian.
Okay I am done now.