Kimagure Goshujin To Oshikake Neko summary:

One day, a beautiful man collapses in front of the home of Araragi Rikuo. ""I'm the cat you rescued last week!"" Such are the crazed ramblings of the self-proclaimed cat boy, given the name Tama by Rikuo, and so their life together begins... Outside of jerking off next to Rikuo in bed, Tama appears to be a cat given human form to stay close to Rikuo just as he says. But, after seeing Tama in a high class suit by chance one day, Rikuo starts to notice discrepancies in their life together and in his feelings...