Rascal Does Not Dream of Home Alone Sister (light novel) — Hajime Kamoshida

GUESS WHO'S BACK? After years without contact, Sakuta has received a letter from his first love, Shouko, asking to meet at Shichirigahama Beach. Of course, now that he's in a happy relationship, he's not quite sure how to respond...or how to explain the situation to his girlfriend, Mai. Maybe he'll just focus on helping his panda-loving, stay-at-home sister achieve her goal of returning to school for the time being. But this is easier said than done, given that she hasn't left the house for two whole years...