Retsu Unohana Enemies

The manifested spirit in Mayuri Kurotsuchi's zanpakutou

Gin Ichimaru is the former captain of the 3rd Protection Squad in Soul Society and one of the three traitor captains who currently lead the Arrancar of Hueco Mundo. A child prodigy whose sociopathic tendencies grew as he matured, Gin is fiercely loyal to Sosuke Aizen.

Hollow Ichigo was created when Ichigo went through a incomplete Hollowfication process.

Kaname Tousen is the former Captain if the 9th Protection Squad of Soul Society and the current vice-commander of Sousoke Aizen's Arrancar army. Tousen holds himself to a rigid code of justice. His blindness renders him immune to the effects of Aizen's zanpakuto.

Muramasa is the manifested spirit of a renegade Shinigami named Kouga's Zanpakutō. Muramasa has tapeworm-like abilities that allows him to control other Zanpakutō, Muramasa has since been forcibly cut off from Kouga and is being overtaken by a Hollow he recently forced to become a temporary host.

Sosuke Aizen is a former captain of the Gotei 13, After betraying the soul society, He became supreme lord in Hueco Mundo. He led a huge war against his former allies in hopes of getting the Oken (Kings Key) and destroying Soul Society, but was eventually recaptured and is imprisoned.

Yammy used to be the 10th strongest Espada in Aizen's army but it is revealed that he was actually number Zero.