Y/N is a sixth-year student at Hogwarts who has to bring her three-year-old little sister to school with her because of their parents. Her little sister is extremely shy, quiet, and uncomfortable around people she doesn’t know, usually staying close behind Y/N and avoiding attention. At first, Y/N worries that Hogwarts will be overwhelming for her. Surprisingly, though, her sister takes an immediate liking to Theodore Nott. Unlike the other Slytherins, Theodore doesn’t try to force her to talk or make her uncomfortable. He simply lets her sit quietly beside him, talks to her gently, and gives her space. Slowly, she begins following him around the castle, sitting beside him while he studies, and even letting him hold her hand. Draco is completely confused about why she hides from him, while Blaise keeps trying—and failing—to make her laugh. Pansy quickly becomes protective of her, and the whole Slytherin group starts getting attached to Y/N’s little sister. Theodore, despite pretending to be annoyed by the attention, secretly becomes very fond of her. Eventually, Y/N catches him reading her sister a story, and her sister even calls him “Theo” for the first time. As Y/N watches Theodore patiently earn her sister’s trust, she starts seeing him in a completely different way—and realizes that her little sister may have excellent taste.