I think that the main dude chose correctly in going for Asa because shes gonna FUCKING DIE if he didnt do something about it but that doesnt concern me so... Lets be selfish! :P
Kaede is like a childhood "friend" that you've known since forever almost like a little sister, Ok so she fucked you up a little when you were young and made you're life a LIVING HELL but thats all in the past. She feels so bad for how you were treated and would do ANYTHING for you. Mmmm Mmmmmm Mmmmmmmmm :) (It would be soooo tempting to go for her as she'd be super loyal and a great GF)
Sia... Seeing as im being me... I dont feel any heat from her. >__>
Primula = Ooooohfff... A super kind loli. :P~ *Drools* (Whats NOT to like?)
Nerine is my favourite though just because I feel like she'd have my back no matter what and Demons in the Japanese mindset seem to be different from what Demons in the West seem to be like. (I.E. They're not total CUNTS who try to ruin everything and seem to be pretty pleasant, Destructive but pleasant) I like Omelette = BONUS! :)
Kareha is the fucking looker of the bunch though but her story doesnt go into ANY detail whatsoever so its hard to get a feeling for her but (For the record I always thought she said ->)My My My... Shes STUNNINGLY beautiful!!! (Seriously tempting)
Mayumi is pretty cool, Good looking and funny also for some reason I think that she'd be the 'best lay' out of all of them. She looks like she'd put in the 'effort'! :P
Nadeshiko seems to be a bit of a challenge, Am I up for it? (Who knows but shes definately worth it)
Ama Shigure would be nice but that would be like a slap to the face for Asa so id hold fire... Just imagine the two of them together though! xD
To sum up my wall of text: Nerine would be the one but if I could be greedy id go for a threesome with Kareha and Mayumi! ;)