It's been a whole year since Rin Touno moved to a boarding house in Tokyo in order to attend high school. Back then, the landlord made Rin an offer he couldn’t refuse: if he looked after the landlord’s granddaughter, he wouldn’t have to pay any rent. However, said granddaughter, Mako Kurihashi, turned out to be a sloppy 20-year-old college student who’s not only completely incapable of taking care of herself, but also repeatedly teases Rin for being younger than her! Despite this, though, Rin fell madly in love with Mako at first sight, and he's been taking care of her ever since they began living together. And little did he know that Mako feels the exact same way about him.