help please

Hi, can someone help me find the name of this manga?

It’s a school romance. The male MC joins a school club where there is only one girl, and she is the only member. She is searching for her “destiny boy / soulmate.” Later she realizes that the MC is actually the boy she has been looking for.

They have a backstory from childhood: they met in a hospital when they were kids. The MC was visiting his older brother named Sei, who was hospitalized there. The girl didn’t want to drink her medicine, so the boy drank it to cheer her up. They meet again years later in high school.

Does anyone know the title of this manga?