Arcas (アルカス Arukasu ) is a creature that protects the entrance to the Fountain of Polaris and Chariot's childhood companion.
Arcas resembles a gigantic polar bear with a golden badge in the middle of the face. He is the protector of the Fountain of Polaris and fiercely attacks anyone who approaches it. However, it retains its affection for Chariot. We know this because it doesn't try to kill her.
In Greek mythology, Arcas is the son of Callisto.
- Arcas's badge resembles that of Alcor's, Ursula's familiar (and an eponymous toy of Akko). Likewise, the four-pointed star adorns Chariot's hat and appears on the breast of Chariot's bird form. In "Yesterday", it is revealed that Arcas was Ursula's childhood pet.