Fuuka is the true name given by Tonbo's soul within Kano's mental landscape. It is unclear how independent the two are. Fuuka may be more than just Tonbo's soul and actually also contain the other 1000 souls meant to be absorbed in the Ritual of Bonding.
Fuuka reveals to Kano that the interrupted ritual left some of Fuuka's/Tonbo's soul in her body and robbed Tcaolin of much of her power and that killing her Champion would kill Tonbo/Fuuka, leaving Tcaolin without a potential vessel.
When Fuuka chose Kano as her Champion, she met him in on Earth, but it seems that Kano was not the one in control of the body at the time. The ramifications of this, if any, are unclear.
After hiding in Kano's mindscape, she roams until she meets Orbkiller in the Snowfield Zone. Orbkiller helps her escape the zone, and after this she meets Kid in the Warehouse and is pursued and attacked by the Breaking Noise. She dreams of Sigmr Ch'k and awakens to her sword as his Champion. She confronts Dark, wakes up Nadia, and then leaves alone for Hell where she rescues Kano from the monstrous Karen.
Fuuka looks much like Tonbo, with dark skin and long hair. However, her hair color is not the same as Tonbo's, varying between blue, blue-green, and a mix of purple and blue-green strands. She does not have Tonbo's facial markings, which signify servitude to Tcaolin.