Stick with the names if you can't figure out when/how to use the proper pronoun unless the characters are written to be able to shape-shift at will it is very frustrating as a reader to constantly have to correct inconsistencies as you read a story. The immersion of the story becomes jagged and broken, thereby interrupting the natural flow and causing irritation.

A ring to control the green power of will oops I mean fire... yeah

inheritor of the system

truck-kun a reliable one way transdimensional transport(no-refunds)