Eiji Yariba is a 29-year-old sales team coach working at a call center for Arcadia car insurance at the Hachijou branch in Tokyo. Although he sees himself as nothing more than a corporate slave, he is widely recognized as the call center's ace and admired by all his juniors. One weekend, free from his work, he bumps into a high school girl in a manga cafe. They find common ground as book lovers, especially since the 15-year-old Karen Minamisato aspires to be a writer. The underage girl soon develops a crush on Yariba, who is forced to turn her down.

Thinking that to be the last he would see of Karen, Yariba is in for a rude surprise when the CEO of Arcadia's Japanese subsidiary, Takayashi Takamishi, personally orders him to "court Karen Minamisato." As Karen’s grandfather, Takamishi wants his grandchild to find happiness, and he has never seen her as lively as when she was with Yariba. Although the CEO's order is later downplayed after a horrified Karen learns of her grandfather's actions, he still insists that Yariba become Karen's friend and keep an eye on her. Eiji Yariba soon finds himself juggling huge challenges in the sales department, in his personal relationships, as well as in his task of maintaining a non-romantic relationship with Karen while developing her writing.