There is nothing else known about Yohanna other than being an associate of Oz Pone Max Reinhardt in the past.
Act 16.6: The Ruins Beckon!
Yohanna let her combat drones know that their father, Doctor Oz, was on his way.
Act 16.9: Mass-Produced Weapons of War
As Oz figured it was her that can use the ancient demon guardians or mass-produced combat drones, Yohanna made a cynical remark on how it has been years that she cannot believe he was still alive all thanks to her according to the doctor. She observed that Oz seemed to have acquired strong allies and it was looking like there was no choice but to run thus before fleeing, Yohanna told him that she believed she found the clues that will lead her to the thing that stupid Bounty Hunter hid. On top of that, she informed the Grand Chase that these combat drones will not be eliminated unless they are destroyed at the same time.
Act 18.4: Reorganize Battle Line
In a flashback, Oz was awed by the sight of the ancient demonic city when Yohanna came to introduce herself professing her pleasure to be working with the doctor.
Act 18.6: Artist's Performance at the Army
In a flashback, Oz fretted if his cursed research that nobody should know about goes out, unaware of Yohanna listening in the distance.
Act 18.9: Commander's Identity
Zero felt familiar energy hence Oz presumed that Yohanna was here. Sooner or later, the Grand Chase encountered her once again with the doctor figuring out that the thing Heitaros was looking for was in the Underworld to which she has confirmed. Knowing it was close by, Yohanna groaned for not thinking that the Bounty Hunter would hide it in the Underworld before running away. At a loss about what was Heitaros plotting, she sneered at them for thinking they can understand his thoughts.
Amidst the battle, Oz hustled Zero to attack Yohanna but hesitated much to the doctor's dismay, reasoning that he was going to kill her anyway. To her amusement, she continued belittling the two of them saying the soldier to catch Duel was used like this when out of nowhere, Lime jumped on her. Yohanna was abashed for not thinking she would lose like that and at the moment that it was Oz's turn to mock her for relying on her dolls, she shall listen to the doctor's advice next time.
Act 22.1: Infiltrate! Underworld City
Yohanna commanded someone to take care of the invaders as she has to find something and has things to do, stating further that Heitaros waited for a long time and they cannot make him wait for more.
Epilogue 6.1: Swaying Ambition
Failing not to let anyone in, Yohanna carried on saying she cannot trust Haros and how they can betray Heitaros but Oz told the commander that she misjudged them if she could not read their uneasiness. Yohanna wanted to know if the doctor brought everyone again and claimed to have remembered all of his battle tactics, adding that it will not be easy this time.
Weary of Oz who kept getting in her way, Yohanna questioned him if he was scared to see the result of his experiment. After the doctor told her his experiment ended with Grandark, she said it was just a sword and that ancient demons' powers are more than the sword, mentioning that he knew better. Oz reckoned that Yohanna desired for something unnecessary, asking her if she wanted to start a battle again or him to destroy the demons. However, she insisted it was the opposite as the Demon God will create the world around Elyos and then demons will prosper. Having lost her bearings, Yohanna mistook Rufus as Legis.
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