Metastacia

is an experimental Hollow used by Sōsuke Aizen an unknown number of years prior to his defection from Soul Society.

Appearance
In his natural state, he exists as a six-limbed creature with a large, flame-patterned mask and a flock of tentacles on his back. When fused with a body, the body takes on characteristics of his appearance such as his black eyes, the flame pattern around them and a grayish green skin color.

Personality
Metastacia was a particularly cruel Hollow, taking joy in eating Shinigami. When Kaien Shiba asked if he had any regrets about eating anyone, he said he had a heart and was filled with many regrets such as not eating Miyako Shiba's head or torso.

History
Some time ago, Aizen focused primarily upon transforming Hollows into Shinigami, and he succeeded in creating Hollows that were close to Shinigami, such as Metastacia.

After Miyako Shiba is sent out on a reconnaissance, her squad was attacked by Metastacia and killed the entire team. Kaien Shiba, Rukia Kuchiki and Jūshirō Ukitake take off after the Hollow. As they arrive, Metastacia had eaten his way out of Miyako and had returned to his original form. Metastacia said then that he smelled fresh meat though it did not smell to bright to him. . Kaien Shiba approached the Hollow and asked how many Shinigami he had eaten. Metastacia told him that he did not keep track and Kaien asked if he even had any regrets. Metastacia answered that he had a heart and of course had regrets such as that he regretted not eating Miyako's head or torso. Kaien attacked Metastacia, cutting off one of his tentacles but then touched the Hollow, causing his Zanpakutō to break. Even without his Zanpakutō, Kaien continued to attack Metastacia, cutting off another of his tentacles. After a little, Metastacia told Kaien that he was a decent fighter even without his Zanpakutō and then uses his body fusion ability on Kaien, launching his tentacles at him and overtaking Kaien's body as his Hollow body crumbles. Rukia called out to Kaien but Kaien, now fused with Metastacia, turned to him and asked what she wanted, calling her a little girl.

Metastacia, in Kaien's body, attacked Rukia, trying to eat her. Ukitake jumped in to save her, telling her to run and she took off. Ukitake attacked the Hollow and said he would find a way to separate Kaien from the Hollow but Metastacia said that their fusion was permanent and that they would be joined forever. Realizing there was nothing he could do, Ukitake resolved to cut Metastacia and Kaien's body in half. As Metastacia attacked though, Ukitake's illness set in but the Hollow went past him and headed for Rukia, who had come back. As he approached Rukia however, she gained the resolve to kill him. As Metastacia died, he returned to Hueco Mundo as Aizen had created him to and Kaien was still a part of him. Once there, Aaroniero Arruruerie absorbed him and gained Metastacia's and Kaien's abilities.

Powers and Abilities
Spirit Body Fusion: Metastacia was able to fuse with a person's body by firing his tentacles at them. The tentacles would work their way into the person's body and infect them, changing their appearance and then causing Metastacia's body to fall apart. When Kaien Shiba was fused with the Hollow, his skin turned green while his eyes turned completely black and orange splotches appeared around their eyes, similar to the appearance of Metastacia's Hollow mask.

Zanpakutō Destruction: If anyone touches the tentacles on Metastacia's back, their Zanpakutō will be destroyed instantly. This effect was limited to once a night, and was the only reason he had such an easy time against a Shinigami lieutenant.

Trivia

 * In the anime, Metastacia did not outright kill Miyako but rather fused with her. In her body, he returned to the division and at night, began killing several members of the division before Kaien arrived and Metastacia took off. By the time Kaien caught up to the Hollow, he had eaten his way out of her body.

Quotes

 * "I smell fresh meat. Doesn't smell too bright though! Should be tasteful nonetheless!"


 * (To Kaien Shiba) "I, like you, have a heart! Thus, there are nights when I feel regretful about the Shinigami I ate. Even now I feel regretful about what happened last night. Especially about that female Shinigami last night. I didn't eat her head or torso. I really regret not doing it!"