The Hill Dyed Rose Madder

One day Junichi Nagase comes across two boys tormenting Yuuhi Katagiri. When he steps in to help they run off calling him "Geno Killer". He then walks off without introducing himself or allowing the girl to either. The next day to both of their surprise she is introduced as a new transfer student to his class. The following day due to a misunderstanding he kisses her which greatly upsets her. That evening to his surprise and dismay she shows up to his door saying she is his fiancée and that she has come to live with him to evaluate him to see if he is worthy of her. Much hi-jinx ensues as the days go by.

Synopsis from Anime News Network