Nodoka no Niwa

This is a love story between 23 year old grad student Asahina Motoko and her 64 year old professor Sakaki Ikuo. Motoko is a very mature and serious girl with poor social skills and is often called dark and gloomy by her classmates. However she finds Professor Sakaki to be kind and easy to talk to, despite his reputation as a strict and scary teacher. Although Professor Sakaki tells Motoko that her feelings for him are not love, something is developing between the two of them, and it might change them both into better people. (Source: Manga Updates)