Continuing the trend for Shaman King, this will be the last character from the anime for now.

Anna is an Itako and the wife of Yoh Asakura, not self proclaimed but actual wife, she appears early on with strict ambitions of training Yoh to be Shaman King much to his dismay at least at first.
A defeat at the hands of Faust and a draw against Tao Ren soon made Yoh listen.
Anna started as an orphan with her abilities unintentionally creating oni that caused mischief and attacked people, Yoh would help subdue the oni that kept tormenting Anna leading her to develop romantic feelings towards him.
Having toughened up as she grew up, she made it her mission to see to it that Yoh is made Shaman King, while her tough love approach seems a bit too far from a viewers perspective and certainly through Manta, it's done out of love, something Yoh returns the night before the Tournament, heavily implied that they did more than sleep together.
This quote sums it up best.
"I'm hard on you, because I know what you are capable of" and Anna certainly understands that better than anyone else.