In the anime Bleach, the Espada (“Ten Blades“) are the top-ranked Arrancar in Sosuke Aizen’s army of Hollow-Shinigami hybrids, they are the most powerful Hollows under Aizen’s command, and are the main rivals of the Shinigami. The Espada consists of nine males and one female. Each Espada member is chosen for their superior combat ability and then assigned a number from 1 to 10 (1 presumably being the strongest) that indicates their rank and relative power level, which is tattooed somewhere on their body.
Shinigami (death god) are a race of spiritual beings that acts as enforcers and psychopomps who all share similar supernatural powers. They are souls with a high level of innate Spiritual Energy, recruited from the ranks of the residents and nobility of the Soul Society. Like all spirits, they cannot be detected by normal humans. Shinigami use their Zanpakuto, supernatural swords/katanas that are the manifestation of their owners’ power, to perform soul burials on Pluses. Shinigami also use their Zanpakutō as well as magic known as Kido to fight their arch-enemies, the Hollows.