Art by kittywithmittens on FurAffinity
Ion has a rare affinity for 2 elements, Lightning and Fire. While he is a master of Lightning Psynergy (I like the Golden Sun word for magic), his Fire is a little lacking (he has decent Fire Psynergy power but nowhere close to his Lightning). Here Ion is fully constraining of improving his Fire Psynergy, being in a dark room and focusing all of his energy. He is then amazed when he was able to create a small powerful sun in his hand as he continues to think how much farther he could go.
Forbidden Sun is a reference to a Dark Souls powerful Pyromancy