How to Upgrade "Flame of Misspell"?

[djmuse1231]

I've polished off just about all the new content off the new update, which I guess means all the content of the game in general, including the final secret character. However, when I was playing him and highlighted the "Beginning" arcana, I saw that there was another icon next to his starter weapon (his starter is a new weapon, a red fire called "flame of misspell," but next to it is a black version of the fire sprite) leading me to assume there's a way to UPGRADE his weapon. Does anyone know how to do so? What are the conditions to evolve his weapon?

[Nikolaus]

Maxed Toronna's box (the gold bar).