Asterius is a large Xenos, described to be more than two meters tall, with jet black hide, red horns, boulder like muscles, and wears full plate armor that's somewhat small for his size, making it seem like light armor.
Asterius has a love for battle, often grinning when fighting multiple opponents, especially if they are strong. Ryuu noticed that he had a desire to fight rather than to kill like normal monsters. Besides this, he is also shown to be very protective of his fellow Xenos, going so far as to fight off the Loki Familia in order to protect them from further harm. He has a deep interest in Bell, due to their battle on the 9th Floor during his previous life, and considers each other to be rivals. Despite his lust for battle, he himself knows he is no match for Ottar.
Asterius was originally the Minotaur that Ottar trained for Bell to fight. It was unintentionally released and ultimately defeated by the boy.
High Resilience: Asterius' body is highly resilient to attacks, capable of not receiving any damage from the Ganesha Familia's attacks, and was able to withstand a berserk Tione's attacks.
Howl (咆哮): As a monster, Asterius is able to howl, preventing unworthy opponents of fighting against him. Depending on the target, it can either knock them unconscious or make them lose the will to fight.
Equipment: Asterius wields a huge double bladed battle axe and wears full plate armor. The plate armor is somewhat small for his body size, making it seem like light armor.
Magic Sword: Asterius owned an axe shaped magic sword that cast lightning magic, though he lost it when his arm was cut off.
- According to Asterius, he named himself Asterius, meaning lightning, because of the crimson lightning he saw at the end of his dream, which was Bell's Firebolt he used during their battle in volume 3.
- Asterius is the name of the Minotaur of Crete in Greek mythology.