- "'She' gets easily bored by this... ordinary type of battle..."
- — Endrance —
"Mia" is a small white cat that can always be found perched on Endrance's shoulder.
Endrance's faithful companion, Mia accompanies Endrance everywhere he goes and seems to possess a will of her own. Though she is incapable of speaking, Endrance appears to understand her and refers to Mia as "She" or "Her" whenever he speaks about her. During Arena fights it is usually Mia that tells Endrance when to activate his Avatar and end the fight. Her presence also gives Endrance the ability to manipulate AIDA.
When Endrance was defeated by Haseo and Skeith during the final match of the Demon Palace Tournament, Mia slipped off his shoulder. Destroyed by Skeith's data drain, Mia revealed her true nature as an AIDA and dissolved into nothingness. The loss of his friend caused Endrance to fall into a deep despair. Depressed he sealed himself away in a remote corner of The World, where he was later rescued by Haseo.
In truth, Mia was just an AIDA made out of Endrance's memories. Seven years previously Endrance had controlled a PC named Elk in The World R:1. Elk had become attached to a PC named Mia, who was in fact a host for the Phase Macha. When Macha was captured by Jyotaro Amagi and Jun Bansyoya for their RA Plan, Mia was lost forever, leaving Elk all alone. It is assumed that AIDA, being interested in humans, began to observe Endrance and eventually took the shape of a small cat that resembled Mia from The World R:1 in order to manipulate him.
In the real world, the player behind Endrance had owned a pet cat named "Mia". When Mia died, Endrance was heartbroken and fell into a depression. Taking advantage of this, AIDA approached Endrance in the form of his dead cat. Believing it to be Mia reincarnated Endrance allowed himself to be taken by AIDA. However AIDA's hold over him was lost when Mia was destroyed by Skeith's Data Drain during Endrance's fight with Haseo.