Riu Tanen is a typical boy surviving in a shelter after an alien invasion claimed his parents. He shares his refuge with his ailing grandmother, diligently tending to her needs. His personality shines as bright and steady, marked by resilience that surfaces in fleeting smiles during hardships—a quiet defiance against the terror of losing his remaining family.

In the "Small Hands" narrative, Riu experienced memory alteration, erasing all recollection of Shizuka upon her approach. This fabricated reality cast him into an artificial mother-son bond with Ana. Within this constructed family unit, Riu and Ana unwittingly harbored the alien entities Yugra and Miysis, disguised as benign houseguests in their home.