Su-ae Shim has spent years dating her indifferent boyfriend, Minu Kang, wishing she could be more like her charismatic stepsister, Ra-im. But everything changes when she discovers Jellypop, a sentient flip phone with plenty to say about her love life. As Su-ae grows distant from Minu and gets closer to his friend, Eunhyeok, she begins to suspect that Minu and Ra-im are hiding something. Can Su-ae survive the twists and turns of high school romance?