 FAIR: Haruka and Keitaro both refer to the same woman as their  grandmother, yet Haruka is Keitaros aunt. This would make Haruka  and Keitaro cousins, not aunt and nephew. In fact, they are cousins.  Harukas parents died in an accident and she was adopted by her  grandmother; thats why Keitaro calls her aunt. (This is not  explained in the series, though)