Mio Hio is a character that only appears in the anime adaptation of D.N.Angel.
Mio Hio is a living voodoo doll created by commissioner Hiwatari, and a pawn in his plans against Dark Mousy and - by extention - Daisuke Niwa. Mio is given the appearance of a student Daisuke's age and given the false background of a transfer student from America.
Her body is only a temporary form with a limited existance. In order for Mio to obtain a "real life", Hiwatari tells her that she must sacrifice someone, Daisuke, by getting him to wear half of a pair of a powerful charms that would steal his soul. Mio makes a number of attempts to do this, however as she gets to know Daisuke, she falls in love with him and decides she doesn't want him to die.
Mio gives the pair of powerful charms to Riku to put on Daisuke, however she comes to regret this action. Mio then attempts to get Riku to give back the charms, by "trading up" for better ones - and when she fears that Riku is (unknowingly) going to use the charms to steal Daisuke's soul she rushes out to stop them.
After more attempts to take back the powerful charms, Mio eventually sacrifices herself to save Daisuke.
Mio makes one last appearance in the end, requesting the help of the Harada twins so that she could do one final thing. Borrowing their strength, she is able to come out of the charm - that she had earlier sealed herself in to save Riku and Daisuke - and confronts Hiwatari. She tries to save him from being consumed by the Hikari artworks, but he ends up being injured by Dark and Krad's fight. Mio returns to the Harada twins afterwards, thanks them for their help and asks Riku to pass on her final words to Daisuke, before disappearing forever.
Takeshi is displayed as having a huge crush on Mio and often spied on her, but Mio showed no affection back unless she could use him to her advantage.
She is told to pretend to have an enormous crush on Daisuke, but really regrets her actions towards him, knowing that they are just to eventually destroy him. She proves her worth by protecting him from the charm Riku tries to give him, sealing herself away instead.
- In the English dubbed anime, Mio speaks with an improper or slangish version of the English language, and sports a stronger accent than other characters.