Nyan Koi!

Synopsis

Junpei receives a letter from Nagi Ichinose, an upperclassman of his, who challenges him to a duel, but since he ignored this letter for three days, Nagi passes out due to stress. During a downpour, Junpei, Kaede, and Kanako take an unconscious Nagi to her house, which so happens to be a mansion of a yakuza. Jii, Nagi's grandfather, treats the three to his home. While there, Junpei is requested from Josephine, a cat owned by Nagi, to make Nagi fall in love. While Kaede and Kanako are taking a bath, Junpei is sent to Nagi's bedroom, where he is surprised to figure out that Nagi is a girl who is in love with Kaede and she also fears lightning due to her past encounter. She was also devastated when her first crush turned her down for her boyish appearance. After calming her down, he departs from the mansion, with Josephine satisfied by the fact that Nagi will now act more feminine.

(Source: Wikipedia)