Ooumi, Megumi

She has a very kind-hearted personality, and sees Tio like a little sister, often calming down her fits of rage and helping explain the world to her.

Megumi first met Tio when she found her injured on the docks. At first, Tio had kept harshly to herself when they'd first met, saying that Megumi would only get hurt helping her fight off Mamono. They eventually started to get along, and Tio came to trust Megumi.

After being helped by Gash and Kiyo, Megumi saw them as friends, like Tio, and swore that one day they would return the favor.

After Clear Note returned to the Mamono World, Megumi can be seen visiting Gash and Kiyo with a lonely face, having missed Tio.

A month after the battle to decide the Mamono King ended, with Tio placing 5th in the battle overall, Megumi receives a letter from Tio and tearfully reads it.

(Source: Wikipedia, Zatch Bell! Wiki, edited)