Un-Sin are a type of beastie in the Metal Shadow universe. They are humanoid figures with high intelligence, taller than the tallest human, around ten feet, with pale, mottled skin and sunken faces. Their eyes glow blue or red. They wear ragged, hooded cloaks to conceal their appearance and often carry tall magic staves.
The Un-Sin first appear in Metal Shadow Prelude. They rescue Noa Rylie, a child they raised into womanhood, from her Elf Squad pursuers. These Un-Sin live in a tribe village far removed from both society and the surrounding wilderness. There, they tame the less-intelligent beastie and practice elemancy. They are the only beastie known to be explicitly capable of this.
The tribe Noa was in told her of Dr. Dragon's intention to remove her latent powers via a parasite, as well as how to extract the parasite. They were then attacked by half-men and bellingsnare under the command of Golden Stanlie. They save Noa by distracting the attackers long enough for her to escape on one of their Sin cloaks. They were losing the battle when she fled.