My Life as Inukai-san's Dog.

On a rainy afternoon, a male high school student awakens freezing on the streets with no memory of how he got there. His classmate and crush, Karen Inukai, finds him and takes him back to her home where, to his surprise, she starts to undress. She seems intent on bathing with him, though he has no idea why. When she holds him once more, he catches a glimpse of himself in the mirror—discovering that he has turned into a dog!

Inukai adopts the puppy and names him Pochita. Now, he must adjust to life as a dog and figure out how to get out of this strange predicament. But while he mulls over an escape plan, Pochita sees a whole new side to Inukai that he never saw at school.

[Written by MAL Rewrite]