Prison of Thanatos

The Prison of Thanatos (タナトスのプリズン Tanatosu no Purizun 死の神刑務所) is a magical prison and the toughest. It's the end of the line to the Dark Mages that committed the most awful crimes.

Overview
The Prison of Thanatos (named after the Greek god of death, Thanatos) was built in the middle of high sea, the Ghost Sea (幽霊海 Yūrei Umi). It is made out of a grey stone with special magic properties, where no intruder can enter. People with pure hearts can't either. Every cell is kept with a seal, each unique to the different magic each prisoner possesses.

It was first founded by the First Siren Feather's Guild Master, who was able to create buildings from water. Currently, the prison has its own policies, having no real owner.

History
The Prison of Thanatos's concept was first though several years before the creation of the first Mage Guilds. With few laws implemented and several Dark Mages on the wild, the world was full of fear. The First Guild Master of Siren Feather and grandfather of the current Guild Master of the same guild (Takiara Chuteaurraux), Carmoiss Chuteaurraux.