Yeijiro has been a friend of Kasashi's since childhood. Both of their families are affiliated with the Guardianship. The Syntans were occasional freelancers and the Akechis run a museum that is actually more of a storehouse for magical or potentially dangerous artifacts. Yeijiro is next in line to inherit/run the place. He is a very talented mage, but is incapable of becoming a Guardian because of his family ties. His spells and magic draw off of the stored power of the museum itself, and range between violent attack spells and healing charms. He is also a talented swordsman, who bests Kas as often as she defeats him.

Yeijiro's a very calm, level-headed person who occasionally comes across as a stick in the mud. Kas and Lynn have entirely too much fun teasing him about it. Nevertheless, he's the voice of reason in a crisis, and there's no telling how things would go without him around to be the strategist.