Nakaimo - My Sister is Among Them!
Available on Prime Video
In accordance with his father's will, Shougo Mikadono transfers to the school that his future wife is said to be attending. But also attending the school is Shougo's younger sister who was separated at birth, and he doesn't know what she looks like - but she attempts to get close to him without revealing who she is! Can Shougo figure out which of the girls at this school is his sister and find his destined life partner at the same time?