Just some screenshots of Krystal in game. Yes, she's fighting Marcus. Marcus doesn't actually have any role in the story and serves as a strong bonus boss. Marcus and Krystal are what I like to call "High flying characters". Basically, Marcus and Krystal have moves that involve a lot of leaping or jumping high into the air as evidenced by one of the screenshots.
Marcus will also use Krystal's staff, later. The Staff combat isn't perfect, so there won't be screenshots of that, for some time.
This is the same as Screenshot 2, except it shows how far from the ground, Krystal and Marcus actually are.