This ship is meant to be the Sunshine!! version of NicoMaki, honestly. And I believe NicoMaki came about before the anime even aired - actually, think way back to when the Mogyutto "love" de Sekkin Chuu! PV first came out (which is when I started to ship them as well), so it wasn't based off of the few interactions they had in the anime. I think the creators caught onto that and added a bit more fuel for the ship in the second season though. If I remember correctly, the old PVs were also how the EriUmi pairing came to be as well.
Nico's popularity... I don't understand it very well myself. I suppose it's because of how eccentric her character is (stalking, tsundere, trying to act more superior than she actually is, but she is also quite dedicated, kind and caring underneath).
last edited at Sep 3, 2016 8:14PM