Painful cries echoed throughout the tunnels as the flames rip through Envy's skin. He writhe and howled as Mustang relentlessly scorched The Homunculus. "S-Stop! STOOP!!" Envy's voice breaks, no matter how much he tries to hide it he is clearly on the brink of tears by this point.
The Flame Alchemist stopped but not out of mercy yet to examine the vile creature before him. What he sees isn't anywhere close to human, despite reverting back to his humanoid form. 90% of his skin was burned off and all he sees is a half-burned carcass struggling to get his bearings. "Did you show him any mercy?" His voice was low and cold yet Envy can sense the threat of something worse coming from Mustang's voice.
He snapped his fingers and the flames consume Envy once more. There was no enjoyment from his actions, he's not a psychopath like the monster before him, for Mustang this was an act of Justice. So he kept on and on till all that remained was a charred skeleton of Envy that laid motionless. Mustang could make out whimpering sounds. It was faint but clearly audible. He sees a tiny creature crawling out of the eye socket of the burnt husk.
Part of Mustang was surprised at this sight. It was so small yet he has caused countless suffering. Responsible for the waking nightmares that will forever haunt his mind. This pathetic little creature made an adorable little girl grow up without a father. Who knows how many other lives or families he has destroyed.
"Damn it.....This again"
Mustang scowled at its attempts in trying to crawl away. (No...There is no escape) he walked over to Envy and pressed the bottom of his boot ontop of him. "So this is your true form? You're ugly. Envy means jealousy. That is what it means right? I get it" he presses his boot down harder
"Please don't" Envy begged
Mustang closed his eyes, he thought about Maes, all the countless victims that were harmed by these demons, the corruption of Bradley. And gradually all that anger vanished. In that moment he had an epiphany. The world needs a leader, a leader that will protect the innocents from monsters like this one.
He removed his boot from The Homunculus and backed away. It sniffled and blinked away the tears that were forming. "You think this is vengeance? It's not"
Envy's body froze with fear, he looked up at Mustang. From that moment he knew that begging was futile, the only option he could do was run.
Its too late. With one final snap Envy is engulfed in a wall of flame. The one thing he'll never forget were the screams, the ear piercing screams as he silently watches the being consumed within the fires he summoned. As the flames are gone there was nothing left. "That's Justice"
Note: So I thought this would've been a much better scenario than what the series provided. My one beef with the series is that it's one thing if it were just Edward who tried to pull that "If You Kill Him Then You'll Be Just Like Him" nonsense but everyone including Riza doing that? Riza?! If there's anyone who'd sympathize with what Roy was feeling then it would be her. Then there's the BS on them accusing Roy of being a monster for his attempt? To me I chalk it up to the writer found Envy too cool to be killed by logical means so lets shoehorn some forced sympathy BS to make him be a tragic character. Then have the characters sympathize with him. Dumbasses, he left a little girl fatherless!!!! FUCK HIM!!!
So I opted out Ed, Scar, and Riza getting involved because I probably would've resorted to some minor character bashing on Ed and I wouldn't do that because I like the character. Plus I would've given Riza a backbone by having her side with Roy. Scar would've been like "You do you Fireman". Cause why would Scar give a shit? Which is why I had it that it's Roy who come to the realization himself on why he should do this then decided to still execute him but in the name of Justice for all the people Envy has hurt.