Ninkyou Neko Choko

This selfless, aggressive kitty cat wants to repay his debt with his body?!

Recently heartbroken Rin (26) turns to his beloved pet cat Choko and sighs out, "If only you were human, I'd just date you." That very same night... Choko turns into a burly honorable-gangster type, and he intends to repay Rin's kindness with his new manly body, no less!! "Go ahead, young master!! I await your command!!" ...Yikes, that's a scary face!! Rin can hardly recognize the adorable black cat he knows, but Choko sounds serious, and seriously fired up to take things to the next level...?! "Compared to some female human... I know you so much better, young master." This tale of duty, devotion, and heavy "petting" between a straight pet owner and a man (cat) of honor determined to outdo his master's exes will have your heart throbbing!!

(Source: MangaPlaza)