Younger brother of Shun. He is from Canaan, a town in Agartha.
His encounter with Asuna occurred while he was attempting to retrieve an ancient stone called the "Clavis" that his brother had left in the underworld. Unbeknownst to him, Asuna followed him to Agartha along with her teacher. This prompted the village elder in Canaan to order Shin to kill her. However, instead of killing her, Shin guided and protected Asuna throughout her journey, all with the same goal of finding the truth about his brother, Shun.
[Spoiler] At the climax of the story, when Asuna and Shin manage to catch up with Morisaki in the deepest part of the Finis Terra abyss, Morisaki trades Asuna's soul as a vessel to revive his wife's soul. Shin, unwilling to lose Asuna, destroys the ancient stone "Clavis," which can grant wishes. Shin finally succeeds in destroying the stone, and Asuna is brought back to life. [/Spoiler]
[Spoiler] Despite having the opportunity to go with Asuna to the upper world, Shin still chooses to live aimlessly with Morisaki in Agartha because he feels guilty for breaking the taboo. [/Spoiler]
