With the release of Tekken 7 has come a torrent of new information about the game, including a new video showcasing the final boss fight with Kazumi!
In the video, the characters are fighting inside the volcano seen from the cinematic trailer and we get to see Kazumi's two forms. The first, she is relatively normal, in a glorious white gown and she demonstrates some deadly fighting moves.
Her second form is a little more demonic - her skin and hair turn completely white (except for a red stripe down her nose), her whole eyes go red, she sprouts horns from the crown of her head and she gets some very cool demon/fire wings. With this form also comes the use of her familiar, a tiger who does some very serious damage, and some special flying attack moves.
This is some great footage of the gameplay of the final stage. You can check out the video below (sourced from SoloKazama) to see Kazumi in action for yourself: