Marko is one of Peter's right hand men and mechanics. He's commonly seen working on weaponry and vehicles. Marko is a minor antagonist, and mostly appears when needed. He has several weapons, but tends to work on the garage working on his Mitsubishi 3000GT.
The Anime never really focuses on Marko or his personality, but based on a few glimpses, we can assume that Marko may be just as arrogant, sociopathic, and power hungry as Peter.
Marko seems to be addicted to his Mitsubishi 3000GT, and he's always seen tuning it with homemade parts.
Marko's weapons are the M9 Beretta, Frag Grenade, Rocket Launchers, Shotguns, Assault Rifles etc. basically any typical weapon a criminal or mob would wield.
He is however, building himself armor, and currently working on his own plasma weapon.
Marko left the Crestfall Convergence, in attempts for a better life after the groups disastrous defeat. He now works as a mechanic, and his goal is to restore, and rebuild cars for the Crestfall people.
He seems to dislike Peter a lot.
Currently, it is unknown on which gang he serves, as many speculate that Peter or Marko could have their own group, or work for the Crestfall Mafia.
He has a tattoo of a cobra, and a dead man's hand (aces and eight).