Grisaia no Kajitsu S01E03 - Sweet Diet

One day while having fun with her classmates, Amane sprains her leg during PE. Mihama Academy has no resident nurse, so Yuuji, who learned first-aid at his previous school, treats her injury. While he tends to her, Amane confesses how she feels and says "Be my boyfriend." It`s so sudden Yuuji comes to the conclusion she`s teasing him. Amane says in response, "If you won`t be my boyfriend, then I`ll be your big sister!"