Hoshi wo Ou Kodomo: Agartha no Shounen  

Children Who Come from Deep Below, Hoshi wo Ou Kodomo: Agartha no Shonen, 星を追う子ども アガルタの少年

A youthful individual named Shin resides beneath the earth with his older brother Shun in an area referred to as Agartha. At some point, Shun departed toward the surface carrying a crystal, prompting Shin to pursue him and retrieve the item for their subterranean dwelling. During this expedition, he will encounter Asuna, who dwells without her father, and Morisaki, who has lost his spouse.