The Heir of Fenix
The middle Ignis sibling, also the Heir of Fenix. He revealed some of his past to Hero once during the Astor Tournament. Apparently, he is the reincarnation of Emperor Fenix, who burned Chien to the ground during the height of the Ignis Empire. Firmus himself hasn't experienced an awakening, so we remembers naught about what happened but he says that his grandfather died because of a special power known as anima sana, which courses through the Heir.
His family cast him out of the palace after his awakening failed and this is what led him to Macellarius where he began guarding Prince Abyssus.