The mystery hook actually works because the show doesn't pretend it's solving anything, it's just an excuse to spend time with girls who feel like real people instead of archetypes. Shougo bounces between them without grinding the story to a halt for dramatic tension, so the comedy lands harder than it has any right to. You know who the sister is by episode nine, but by then you've stopped caring about the inheritance and started caring about whether he picks the right girl, and that's when it hooks you.

Shougo Mikadono has a problem. His father's will demands he marry before collecting an enormous inheritance, so he enrolls in a new school to find a bride. Sounds manageable until Shougo learns the catch: somewhere among the female student body is his half sister, separated from him at birth. He has no idea which of the girls she is. What follows is a romantic comedy minefield where every potential girlfriend could be family. His sister is quietly trying to get closer to him while hiding who she really is, and Shougo turns out to be popular with the other girls too, from the class representative who becomes his first friend to the student council president and a cafe owner who dresses like a witch. Expect comedy, romance and plenty of ecchi awkwardness built on one very uncomfortable question.