Even though outgoing and bubbly Yuzu doesn't always get along with serious her step-sister Mei, she still wants them to be a family. But when Mei kisses Yuzu, it makes their already complicated relationship that much more complex! That's when Matsuri shows up, an old childhood friend of Yuzu's who is determined to battle it out with Mei for the title of "Yuzu's little sister." What Yuzu doesn't realize is that Matsuri isn't the sweet little girl she used to be, and she's willing to use every dirty trick she can to break up Yuzu and Mei's relationship. Will Yuzu be able to protect Mei from this devious interloper?