Terra Brandford (protagonist) has the ability to morph into her esper form. Why? She's born half esper, half human thus has the ability to shift in between forms at will. She's the only one who can do this as she is the only half esper. Think of it as a DBZ sort of thing--all of her abilities are doubled when she is in her esper form but it only lasts a given amount of time.
Celes Chere, another hero in FF6, was infused with magic at a very young age by the empire and she has the ability to use it. Unfortunately, she isn't half esper, so she doesn't have the ability to morph like Terra can.
Now, what if she could? It would probably look something like this.
Terra Brandford
->
Celes Chere
->
Celes Chere, another hero in FF6, was infused with magic at a very young age by the empire and she has the ability to use it. Unfortunately, she isn't half esper, so she doesn't have the ability to morph like Terra can.
Now, what if she could? It would probably look something like this.
Terra Brandford
Celes Chere