Doutei Hitsuji to Abazure Ookami

Doutei Hitsuji to Abazure Ookami summary:

"I think I fell in love with you, Onii-san..." Tanaka is your average salaryman, who's never had a girlfriend. One night, as he's walking through a park on his way home, he's about to get assaulted when a young punk named Kira comes to his rescue. Tanaka wants to thank the young man for saving him, but Kira only wants compensation... from his body! Shocked to have been robbed of his first time, Tanaka wants to forget it all, but Kira seems to have taken a liking to him and waits for him every night on his path home, like a dog waiting for its master... Will the lamb let it itself be moved by the wolf?