Rank their immortality.

Personally

1) Yhwach (can literally rewrite his death - resurrection and Regen.Died only because of silver arrow)

2) Aizen (Hogyoku can literally won't let Aizen die. The only one with no weakness and capable of resurrection)

3) Ichibei (Won't die because of his connection with reio and his ability. And might be biologically immortal. Insane regen)

4) Lillie (godly immortality and intangibility and insane Regen. Possible to kill)

5) Gerard (Miracle can literally revive Gerard from death. Possible to kill with destroying his cross)

6) komamura (Immortal and indestructible body. Has insane drawbacks)

7) Pernida (nearly impossible to kill. Only died to cancer last stage x 10000000)

8) Askin (Extremely hard to kill because of his ability, even more difficult or nearly impossible if gained full immunity. Being able to survive even after his heart was ripped open)