Inu(1994)

Stars a female college student with a pretty intense sex drive who has an "H mode" not unlike Rena from Otogi no Machi no Rena, though with a great twist: she's only able to enjoy the sex when she has no romantic feelings for the partner. She used to use her sister's pet dog as her sexual outlet, but the dog has recently died, and being a penniless college student, she can't really afford to buy a new one for herself... which is where the gutless, dorky guy who has a crush on her comes in. He's looking for a girlfriend, but she only sees him as the replacement for her dog; hijinks and sexy times ensue.