Sis, How Did You Become So Obsessive?

【Urban Slice of Life】【College Life】【Older Sister and Younger Brother】【Heartwarming Daily Life】【Slight Yandere】【No System】【Not Reborn】 (Author's note: Su Chiyu started out as nothing more than a little sister-obsessed older sister with a strong possessive streak who got jealous easily. After spending a year at college, outside influences did make her a bit yandere, but Gu Yuan, the male lead, will gradually help her heal. That said, her jealousy and possessiveness aren't going to change.) Gu Yuan and Su Chiyu are an older sister and younger brother with no blood relation. After her family went through a crisis, Su Chiyu moved in with the Gu family at the age of seven and grew up alongside Gu Yuan. They have always presented themselves to others as siblings... Over the course of ten years together, they went through elementary, middle, and high school, and are now about to start college together. They seem just like real siblings, but since they aren't related by blood, it seems they both have other ideas. Every night, Su Chiyu would quietly sneak into Gu Yuan's bedroom... Then, after Gu Yuan finished his college entrance exams, he realized that his older sister Su Chiyu, who had gone away to college for a year, seemed to have changed. “What's this?” “This isn't mine! Sis, let me explain!” At the graduation party, someone set Gu Yuan up. Su Chiyu thought he had a relationship with another girl that went beyond friendship, and she finally couldn't hold back. “Su Chiyu, calm down...” Gu Yuan looked at the loving gaze Su Chiyu fixed on him, and her tilted head... Wait... Could my big sister be a yandere?