Inyou is a "Search and Rescue Specialist" in Magmel. (also known as Angler). He is also a Lachter, a person who can use a materialization ability called Lacht.
Inyou's someone who takes advantage of the opportunities when he's given to, to satisfy his own needs.His glare hints there might be a mysterious/sinister side to him this was shown when dealing with The Saintess. He's laid back, unconcerned and doesn't rush through things. Rather, he takes his time to execute correctly and satisfactorily.
Relation with Zero:
Inyou and Zero are typically partners. Zero was rescued by Inyou around Shuin's disappearance. Zero has seems to have romantic feelings for Inyou.
Relation with Shuin:
Shuin's specific relationship with Inyo is unknown. Yet it has been shown that Inyo is Shuin's apprentice or in a similar relationship.