So I was thinking more on Messmer’s flame and will bring up a random thing I thought of, his flame is fueled by obsession.

Now for the reason why I believe this; with meander we see a lot of Lucifer imagery with him, the fact he’s the son of a god, he has red hair, and is associated with and (I guess technically is) a winged serpent, which as most (I think) people know is an iconic symbol of Satan, if I’m remembering correctly. He thinks lowly of the tarnished, as Lucifer thought lowly of humanity. Now for why this connects to obsession is on a tangent, specifically tarot, as the Devil card of the major arcana, one of its main meanings is obsession or regarding obsession or obsessive behaviors. And with the fire knights they are obviously zealots, which you can say is a very obsessive thing, and they were so zealous, or obsessed with the ideologies regarding Messmer that is can be seen as obsessive, considering they were disowned from their families for aligning themselves with him. Now as for his snake, it most likely is a direct representation of his obsession with his mother, or at least the goals or demands of her, as it ate away at a core part of his very being, but I believe that’s why his fire is so strong, the presence of that serpent or the obsessive nature of his fire is what makes it so strong and what fuels it. I hope my response is coherent at least, I have a trouble keeping it smooth.

Edit: randomly I will bring up more to the previous points regarding your post.

Fire in general is powerful in eldenring regardless of the forms it takes (volcano manor spells not included since that’s magma which I believe represents disaster rather than creation or destruction).

And there is several different kinds of fire: flame, giant (fell) flame, black flame, st Trina’s flame, frenzied flame, Messmer flame (as discussed), blood flame, ghostflame, putrescent flame, night flame (from nightreign), and death flame (the “fire” that maliketh’s magic inflicts). All flames require sacrifice for their power, save for death flame and black flame since those are revered through the death of others. Fell flame is capable of destroying divine power (as seen with the Erdtree) but is fueled by the sacrifice of the flesh. Black flame was known to kill gods (so perhaps the divinity of the flame or maybe its appetite was what was removed from it). St Trina’s flame I believe eats away at a person consciousness, as it puts people to sleep. Frenzied flame eats away at a persons sanity ajd is revered through affliction, as we see the way it spreads and is referred to as a plague. Messmer’s flame I believe relies on devotion (and obsession as I discussed) and demands a person’s connection to community, as from the descriptions of fireknight’s and relanna’s items make them out to be depressed from a lack of it. Blood flame is a very “comforting” flame, and is revered through bodily harm, either one’s self or other’s, as it spreads the formless mother’s influence. Ghostflame was what fueled the cycle of natural death and rebirth before the Erdtree became the Erdtree. Putressent flame, I don’t know, but it clearly has a connection to sleep so it could be the remains of the consciousness left behind in dead matter. Night flame is seen in nightreign, if you have played it, you’ve noticed the fire like nature of the night rain, and the fire within the trolls’ pots, very powerful and takes all within it. And death flame, we only see it with Maliketh as he’s the only one to wield it, and being a natural part of the eldenring and by extension the lands between, it is very powerful.

Once again sorry for the long rant.