User blog comment:Jkphantom9/Volume 3 Episode 7 Sneak Peek/@comment-24994749-20151231152305/@comment-26397825-20160101004025

I had a thought about that fire.

Merc's dad is a drunkard. I have picked up undertones of 'crap happened' between Merc and his dad when he mntioned him. Mercury and Cinder are outside, in a mildly forested area, alone, and Mercury is kinda beat up.

I was wondering if Merc's dad went the 'abusive drunk' route, and Mercury eventually got sick of it. He kills his dad (whether on purpose, or just by accident trying to get him to leave him alone), the house goes up in flames and Mercury stumbles away only to meet up with Cinder. Cinder complements his strength, he does the whole "I'm not strong enough" routine, and Cinder offers him a way to get stronger.

Voila, Mercury joins Cinders crew.