Tsuki no Seiyaku to Gensho no Hime

Tsukimi, an ordinary high school boy, receives a mysterious egg from his grandfather. It is the beginning of an adventure that will turn Tsukumi's everyday life upside down. After learning the truth about the moon and the state of the world, Tsukumi sets out to fulfill a promise he made to his childhood friend Yoka that day.

(Source: Kadokawa, translated)