 The are an order of ten arrancar who are the
strongest and most powerful in Sosuke Aizen’s army; each member
represents an aspect of death (according to "Bleach" lore).They are ranked from 10 to 1 based on "reiatsu" density (not necessarily battle
skill or prowess), with 10 the weakest and 1 the strongest.However, the
Espadas are also ranked from 9 to 0, since Yammy Llargo, basically the weakest
Espada, can become the strongest when certain conditions are met.