Mist

Past Timeline
Mist was a heavenly person found by Freyja and used as Freyja's experiment because of her strong power. Freyja tested on Mist and conducted various experiments. Freyja was unsuccessful because Mist's shackles couldn't be controlled as Her mind was too powerful. Mist became too dangerous so Freyja imprisoned her in the depths of the heavenly realm.

Eventually, Mist became more mentally stable but her emotions all gone. Now all she could think was killing her foes. At Freyja's orders, Mist became her puppet and Freyja used her to wipe out strong enemies for her. Mist was giving a final and extra position among the celestial guardians, the eight seat.

Mist once entered the battlefield with mist all around her and she was then called Mist of the Battlefield by the others. It is also revealed that Mist's spirit was actually a female celestial monk named Xuanzang. She was a friend of Sun Wukong before he was exiled from the heavens.

Season 4
In episode 50, Freyja meets with Mercure and asks him to help her continue the experiments on Mist to make her a strong test subject. Freyja unleashes Mist from her cage to stop ragnarok (final battle between celestials) and wipe out her enemies but in reality Mist is likely to bring ragnarok faster.

There was a mention of a goddess who unleashed a beast and the beast devoured many. It was originally believed this was Reginleif unleashing Fenrir but Skuld confirms this was Freyja releasing Mist.

It is revealed in territory 16 that Sun Wukong recognizes her from the past. Mist's spirit and mind actually comes from a celestial monk who had been a companion of Sun Wukong long ago. He's shocked to find out she became a victim of experiments and brainwashing. Mist does not seem to remember Sun Wukong since her memories were completely wiped out. Freyja tried to create the most powerful homunculus by using the soul of the female monk but the experiment failed when Mist could not be controlled or contained.



Trivia

 * Mist is actually the strongest special hero in the timeline, confirmed in June 2020. However, Freyja was able to overpower Mist once, it is likely Freyja has stronger overall power.
 * Mist's concept comes from the valkyrie by the same name. Her name comes from Mist of battlefield or Mist of war. In seven knights, she's not a valkyrie. In her monk form, she's based on xuanzang from a journey to the west.
 * She may be a parallel to Silvesta both being test subjects.
 * She likes 'killing' and dislikes when she is disturbed or interrupted during fighting.
 * Despite having much purple in her design, she probably symbolizes the color black (death, power, mystery)
 * She can be considered a chimera due to her power. Chimeras are the ultimate homunculus.

Season 4

 * Freyja: "Leave me alone."