"Yankee-kun to Nemuru Onee-san" is a Japanese manga series written and illustrated by Kawaguchi Kaiji. The story follows a high school delinquent, known as Yankee-kun, who unexpectedly forms a bond with a sleepy, older girl, Nemuru Onee-san. Their interactions blend humor and heartwarming moments as they navigate their contrasting personalities. The manga explores themes of friendship, personal growth, and the challenges of youth. It features a unique art style and relatable characters, making it appealing to a wide audience. The series has garnered a following for its lighthearted storytelling and engaging character dynamics.