Euan is a ten year old boy with A type blood and a height of 143 centimeters. When he is first introduced, he appears to have lost all memories except for his own name and is found crying under the light of a full moon. He is taken in and protected by Kotono, subsequently living with her and Joshua in a monastery.

On the surface, Euan comes across as a clingy, lively, and affectionate young boy, a demeanor that causes animals to be frequently drawn to him. However, this behavior is later revealed to be a complete act. Contrary to his initial presentation, he has not lost his memories at all, and his cheerful and dependent personality is a deliberate performance. His role in the story is therefore layered with deception, as he hides his true nature and past from those who have taken him in. His key relationships are with Kotono and Joshua, as the three of them share a life at the monastery, though Euan's connection to them is built on a fabricated identity and hidden motivations. His development involves the eventual revelation that his memory loss and innocent persona are false. The narrative does not provide notable supernatural or combat abilities specific to this character, focusing instead on his secretive background and misleading character traits.