Flames make particles.
Flame Texture Item allows you to upload Flame Texture Art
Flame Texture Art is a image that defines shape and color of the particles.

Flames must be forged, either by buying forge access or from someone who has it. These cost 50k and up, most at 100k.
Flame Texture Item is in the shop.
Flame Texture Art can be drawn by anyone, but if you're looking for someone who does graphic designs to do it, it can be requested.

You need all three (unless you use default on Art) for something to appear in game. So, what exactly are you after?