Bankai

Bankai is a technique that increases the users physical prowess and capabilities with the extent of one's mastery over. This technique seemingly like the Eight Gates, therefore has been classified as it's sister technique.

Amaka Date
Amaka, as a member of the Date Clan is a main master in the flow of chakra. She can use this technique, to increase more then one thing at once. Meaning, she can control the flow in chakra in both her strength and speed, a feature not directly granted. Amaka however, is seemingly never ready to use this technique unless in a crisis situation. From what she was stated, no one has ever lived when she's used this technique, and she's supposedly used it twice before.

In her youth, Amaka devoured a shark for food, and was granted all of its abilities. However, there is one feature of a shark, that Amaka employs perfectly with this technique. It's what she calls Shark Frenzy (鮫猛, Kōno), which is based from, and it allows Amaka to enter a state of uncontrollable rage. This allows her to access all stages of the physical capabilities all at once.