Leon wasn't saying that bell didn't work for his power just that if you consider how long bell was an adventurer before he got the skill to how much he grew after getting it the hacks nature of the skill becomes clear. leon knew that there were things that qualified people for the skills they gained but besides speculation no one knew what they were. like leon was pretty sure that his faunus features and his determination to be a demon for the grim were some of the qualities needed for the devil's due skill but he could easily be wrong without knowing it.
What leon really wanted was a magic school skill that let him access a whole school of magic rather than needing him to get creative like his hell fire spell. his current spell as super flexible with how he could use it but it also forced him to create his own variations to it on the fly. a magic school skill would give him access to a huge amount of premade spells that had various different effects , the only downside would be the chants he would need to say perfectly while in combat to use them.
'Since surviving a grim swarm isn't enough of a feat what about clearing the entirety of mount glens ruins?' he thought with a wicked smirk. leon flapped his wings kicking up a small dust cloud from the wind and gained altitude. from far above the city leon memorized the pattern layout before swooping down to the huge broken down wall surrounding the city. 'i'll start by flooding the streets with hell fire killing all of the grim outside before clearing the buildings.' he strategized mentally. with calamity clipped onto his back leon summoned hell fire over each of his hands and pointed down the side of the wall.
Thick gouts of flame burst down the quarter mile tall wall and onto the overgrown street below. like a dreadful hydra of fire the flames spread and ate every thing in their path as they split down multiple streets. it was like the apocalypse for the grim outside in the city as the merciless black and silver flames rolled over them and devoured them hungrily. leon was quickly running out of mana using such a potent spell that required so much concentration. but thanks to the unique property of the spell to allow life force as an alternate source of fuel he could keep pressing it.
Leon was practically drowning in life force as the spell advanced killing an uncountable number of grim. the sheer amount of life force was so great that leon was little more than a human sized blood red lighthouse to those who could see him. the hunters stationed nearby to keep an eye on the local grim population took pictures of leon like this to report later. none of them had any delusions of getting near leon however as anyone with this level of power was not someone they wanted to get anywhere near.
The hell fire had an interesting property of turning more black than silver when fed with solely lifeforce. this meant that despite the fact leon had covered close to a quarter of the streets in flame the glow coming from the city was not stupidly bright. leon cut off the spell after having cleared a quarter of the streets of grim and leapt down the wall to the scorched and melted pavement below. with a little sound thanks to his wings he landed softly and began to focus the maelstrom of life force around him between his hands.
The glow faded as more and more of the energy was condensed together into a glowing blood red handful of liquid. this was an idea that leon had ever since he had noticed how lifeforce seemed to act like a gas when extracted. he wondered if since the stuff could exist as a gas he could convert it into a liquid or even a solid. the biggest problem leon found during his experiments was that he needed a HUGE amount of the stuff to condense even a single drop of the stuff.
Leon crossed his fingers as he swallowed the hand full of liquid in hopes he doesn't just explode from "overeating" as it were. thankfully leons worries were unnecessary as the liquid went into his storage area without any fuss and only displaced an equal volume of the gas state life force which he let dissipate. leon didn't even have time to celebrate his increase in lifeforce quality before a thick greasy black substance started pouring out of his pores letting off a vile stench that immediately made leon throw up.