"One by one, the demons were defeated by the Eight Immortals, the legendary heroes of ancient China."
The Eight Immortals are eight warriors from Chinese legend. In the series, they were the ones who banished the eight Demon Sorcerers to the Netherworld and locked their portals with the Pan'ku Box. However, in their symbolic relics was a portion of the banished Demon's chi that could endow anyone with its power.
The Eight Immortals are actual figures from Chinese legend (Taoism, specifically), being eight individuals who attained immortality and various other magical powers by various means, usually as rewards after being tested by a Taoist sage, Lao Tzu, or another immortal. The magical weapons and items used to banish the Demon Sorcerers in the second season are also associated with them.
In the Demon World Arc, Shendu wrote in the Book of Ages that all the eight Demon Sorcerers were never banished to the Netherworld, altering history by causing the banishment to never occur. Curiously, their symbolic items were still capable of banishing the demons. This meant that they acted behind the scenes to ensure the demons could still be banished, regardless of the historical alteration.
Powers and Abilities
The Immortals were masters of good chi magic and formidable martial artists as well. In the flashback, all of them defeated the 8 Demon Sorcerers with very little effort. They also created the Pan'ku Box to seal the demons' portals. Furthermore, the common items that represent their symbols are capable of banishing the each of the Demon Sorcerers back to the Netherworld.
||Maiden in waiting||Flute||Hsi Wu|
|Crippled begger||Gourd||Bai Tza|
|Patron of actors||Castanets||Tchang Zu|
|Philosopher||Lotus pod||Tso Lan|
|Hermit alchemist||Drum||Po Kong|