Giant Hollow Fortress

The Giant Hollow Fortress is a floating structure commanded by the Unnamed Female Arrancar during an attempt to attack Karakura Town. Its core is the most powerful part, as well as the most fragile.

Overview
This Fortress is made up of hundreds of Hollows, merged together, thus creating a giant Hollow-like building. The fortress is later destroyed by Urahara Kisuke's Benihime, after the Karakura-Raizer Team prevent it from destroying Karakura Town, leaving the full extent of its powers unknown. The Unnamed Female Arrancar perished within the Fortress.

Karakura-Riser Mini arc
This giant Hollow-like building unleashes many hollow, such as Zonzain, who is defeated by Kon's Karakura-Riser Beam. The rest of the Hollow flying above Karakura Town, are destroyed by the other members of the Karakura-Riser Team. It is later investigated by Don Kanonji, and is revealed by Tessai, that the fortress is made up of hundreds of Hollows merged together. The Karakura-Raiser Team head over to the fortress, but are ambushed by Hollows released by the fortress. Ururu Tsumugiya defeats them all. Tatsuki Arisawa, Kon, Keigo Asano, and Chizuru Honshō arrive inside of the fortress. They are ambushed by even more Hollows coming from the fortress, but all are defeated by Tatsuki. An Unnamed Female Arrancar tries to kill Tatsuki, as the Arrancar introduces herself to be the one commanding the fortress. The Arrancar is later defeated by Chizuru.

Kon then runs to the core of the fortress and is then scared by the core's being. Kon accidentally apologises and then attempts to take advantage of the core's inability to move. Before he attacks the core, a Hollow appears before him and attacks Kon with many Bala. Kon uses his Karakura-Riser Beam to defeat the Hollow and destroy the core.

Part of the fortress then blows up, as it slowly approaches the water. Kisuke Urahara then finishes off the fortress with his Benihime.

Powers & Abilities
Summon Hollows: This is the fortress's main technique, as it is made by many Hollows itself. The fortress can summon many Hollows into many different places, such as inside of it, or outside of it. It can even send the Hollows to different locations, such as Karakura Town.