Otogi Sekai no Oosuke(2018)

Otogi Sekai no Oosuke

Oosuke, a high school student, had promised to illustrate a children's story written by his childhood friend Izumi. When Izumi's story wins a prize and the time is finally right, she is attacked by an unworldly creature...? The girl creates the story, and the boy moves it! A battle fantasy of fairy tales!

(Shonen Jump Plus, translated)