The Kid's Leader Who I Thought Was a Boy Is Actually a Girl

She was a tomboy… big emphasis on "WAS".

When he meets his childhood friend again, the one he thought was a boy, he discovers that she was actually a girl, who has grown up to become a beautiful young woman! She takes care of him, they go on a date to the park together, and there are lots of sweet and sour situations!

(Source: Melonbooks)