Grimmjow
Jaegerjaquez

Grimmjow Jaegerjaquez is the sixth Espada and the purest predator in Aizen's army. He was an Adjuchas-class Hollow, a panther who clawed his way up the Hueco Mundo food chain, and becoming an Arrancar did not civilize him at all. He launches his first attack on Karakura Town without orders, loses his left arm as punishment when Tosen enforces discipline, and gets it burned off with a smile. The arm comes back the moment Orihime's rejection power proves useful to him.

What separates Grimmjow from a simple thug is that he needs Ichigo specifically. Their first fight ends with Ichigo bleeding on the pavement and Grimmjow disgusted that it was so easy. Their second is interrupted. For the third he heals Ichigo through Orihime first, because beating him at less than full strength would not count. The resulting battle under the dome of Las Noches, Pantera's release against Ichigo's Hollow mask, is the ceiling of the Hueco Mundo arc, and when Grimmjow finally goes down, still snarling, Ichigo blocks Nnoitra's blade to keep him alive.

That debt gets honored in the strangest way. In the Thousand-Year Blood War Grimmjow steps out of a Garganta as part of Urahara's invasion force, greets Ichigo by slashing at the ground next to him, and announces that he would never die before getting to kill Ichigo himself. He fights the Quincy because they are in the way of that appointment. Nelliel headbutting him mid-threat is the closest thing he has to a working relationship.