Another Dark Mai came into existence when a Possibility of Mai Natsume had a Calamity Factor put into her existence. Becoming a new being with a lust for battle and destruction, Another Dark Mai fell into the service of a certain someone and has begun to monitor Phantom Fields on their behalf.
Alternative: Dark War
When investigating one particular Phantom Field, Mai came into contact with Ciel Sulfur and the two fought against each other. Ciel called her a puppet, but Mai was not phased. The two continued fighting until they were interrupted by Rei. Mai moved in to swiftly kill them, but Phenomenon Intervention occurred and Mai's blow missed. Confused and knowing that there was an Observer in the midst, Mai's attention was turned away from both Ciel and Rei. In that period, the two of them escaped.[1]
Another Dark Mai eventually caught up to Ciel and Rei, who alongside them included Kazuma Kval and Raabe. Ciel asked her if she was their enemy, but Mai did not take well to this, instead preferring that they call her a "villain". She taunted the group, saying that she was going to enjoy stabbing Rei repeatedly. Rei was beginning to Observe her, but Ciel stopped this from happening. As Mai launched more threats of killing the group, Raabe used Phenomenon Intervention to teleport the group to the other side of the island. This disheartened Mai, but it allowed to her to check out more of the island and continue with her objective.[2]