A kind-hearted and mature boy the same age as Amu who serves as the K-Chair (King’s Chair). His alias is “Prince”, as he is a bishounen, and he is Amu’s love interest. Whenever he is called “Prince,” his character changes into a violent, egotistical king who wishes to rule the world. Because of this, he does not do Character Change with Kiseki unless it is absolutely necessary. Actually, he too is a shy person and is not a public speaker. Because of this, he wished to become another, stronger character, much like Amu. He lives in a traditional Japanese house. He had a precious dog named Betty (name learned in volume 2 of the manga) who died recently, and is still upset about it.
He, along with the other guardians, tried to get Amu to join because of a prophecy about a girl who will appear with three Guardian Eggs. At one time he lost confidence, as he could not seem to find the Embryo at all. He was then affected by the Black Diamonds CD, causing Kiseki to change to an X egg. Amu helped him out of this crisis and he is now able to Character Transform with Kiseki, becoming “Platinum Royale”. During a Character Change, his attack is “Holy Crown”, in which he creates a golden shield of energy around himself, where as in his Character Transformation, it is “White Decoration”, which cleanses X-Eggs. When he becomes “Platinum Royale” he has lots of frills and laces. It is said the writer purposely did this to make him more princely.
He had a crush on “Amulet Heart”. He also said that he loved Amu because “Amulet Heart” is her “self that she wants to be”. At first he is about the same height as Amu, but as the story progresses, he grows taller. In chapter 28 and/or episode 74, Tadase confesses that he likes Amu by asking if it was OK to fall in love with her, saying that he has learned Amu really is herself and doesn’t think about “Amulet Heart” anymore. Ikuto, hidden in the closet, hears his confession to Amu. Ikuto becomes jealous of Tadase.
Tadase reveals that he was once childhood friends with Ikuto and Utau. He looked up to Ikuto and called him a brother.