Ōin

The is an artifact that belongs to Soul Society's Royal Family, and is moved from its storing place to a different location every few decades.

Summary
When the Ōin was being transported to a new location. Sōjirō Kusaka and his two Arrancar companions attacked the transport and stole the artifact, despite 10th Division captain, Tōshirō Hitsugaya, guarding the transport. Later on Kusaka tries to get Hitsugaya to stab the Ōin with his Bankai, so its power would be released, but Hitsugaya refuses and Kusaka himself cuts the artifact. Because of this, Kusaka turned into a large, powerful ice dragon, but very unstable due to Kusaka not having achieved Bankai. It took the effort of several captains and Ichigo Kurosaki, but Kusaka was eventually defeated. Afterwards the Ōin was returned to the state it was in prior to being cut by Kusaka.

Powers & Abilities
Dimension Control: If a person has full control over the Ōin, then the person has absolute control over the dimension as they see fit, including the manipulation of time, energy, space, and matter.

Teleportation: Given that the seal can manipulate space, it can give the user the ability to teleport any amount of distance.

Healing: Given that the seal can manipulate time, if the user is hurt, they can transfer their body back to the way it was any time before.

Requirements
For a person to fully control the Ōin, they need to use the power of a Bankai to cut it. If the one who cuts it haven't achieved this, the seal's power will expand at a dangerous rate and cause mass destruction, causing the user to transform into a powerful but highly unstable form.