E-121 Chi was an E-100 Series robot.
Chi was the twenty-second E-Series robot created by Dr. Eggman. According to the Egg Network it has been destroyed, presumably by E-102 Gamma, but due to a memory error the robot has no recollection of this happening. (ASUB)
- Chi was never formally introduced in the comics, but his fate was revealed in the (now defunct) Sonic Universe blogs.
- In the video game Sonic Battle the robot designated as E-121 was known as Phi rather than Chi. According to Ian Flynn, this misnumbering is the real-world reason for Gamma's memory error.