An Esper is a magical being from another plane of existence in Final Fantasy 6 (Final Fantasy 3 in NA). Either through force or by their own choice Espers can transform into Magicite. It's this Magicite that gives most of the characters their magical and summoning abilities. The only exceptions are Terra and Celes. Terra, being born half-Esper, can gain some magical spells on her own while Celes...
It was Kefka's plan to use technology to force Espers into this Magicite state against their will. Kefka would then use this Magicite to create a powerful army that could wield the long dead magic.
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