Hinako and Wakatsuki twins for me.
Hinako was easily the best character this series had to offer. While i find her personality to be slightly annoying , she also manages to be quite cute in her own way. Coupled with the fact she offered some of the best episodes and was one of the few characters that was not mishandled, there is no way i can not vote her.
Wakatsuki twins - the saving grace of the later half of the anime. They share a nice bond, and one can tell they really are close.
Added twincest possibility makes this case stand out even more 
In the end they had very nice dynamics as characters, and Shuu is a pretty good male character, even if i was not that fond of Shuri. Can't have one without the other
