In the first episode of My-Otome Zwei, an unknown entity that petrifies its victims attacks Garderobe and brings the Predecessor system offline once again. However, having apparently learned the lessons of My-Otome, the Otome now have a backup "Surrogate System", which can temporarily power them in case of the Predecessor's failure.
In the second episode, a winged black Fumi-like figure attacks Windbloom City. As the unknown entity has been shown to be able to replicate the shapes of its victims, it presumably petrified Fumi while inside Garderobe back in episode 1. In the third episode, the figure attacks Nina and Nao and is identified as the Pure White Diamond before petrifying Nao. The figure is also seen summoning a sword that greatly resembles Kagutsuchi's sealing sword from My-HiME in front of an egg-like enclosure that appears to contain a creature. The figure petrified Miyu, Shizuru, Miss Maria, Haruka and Nao.
In the fourth episode the entity, now known to be named Yuma, takes the form of Fumi herself in giant form and does battle with Arika and Nina. After the Garderobe staff disrupt the connection between Fumi's body and the entity Yuna takes Mashiro into itself (taking the form of Mashiro's CHILD form, Suisho, from My-HiME in the process) until Arika and Nina's combined attack destroys it. The petrification victims are also restored after this. On an interesting note, the Robe that Fumi (Yuna) wears is similar to Nina's Ultimate Black Diamond Robe, confirming the fact that Nina's GEM is related to Fumi's GEM.
Read more about this topic: Fumi Himeno