Gungrave opens thirteen years after Brandon Heat is betrayed by his best friend Harry MacDowell. He is reborn as Beyond The Grave, and begins a quest of revenge against the crime syndicate. The series then backtracks to Brandon's youth, and follows him and Harry as they rise through the criminal underworld, detailing the circumstances that led to their eventual falling-out. It should be noted that the story is loosely based on Sergio Leone's gangster epic, Once Upon a Time in America.
From a review:
Synopsis: His name is Brandon Heat. Or at least it was. Brought back to life after 14 years, he is now Beyond the Grave. With his sudden resurrection comes the interest of the ruthless Millennion Organization and its even crueler leader Harry McDowell, who seeks to send Brandon to the grave once more. But behind this small war is the story of two young men seeking favor with the mafia, the ambition that further united them, and the betrayal that tore them apart.
Every anime fan that has watched it loves it. It's one of the most critically adored anime shows ever (I can't think of another show that has gotten more 10/10's besides Cowboy Bebop and Death Note).
Edit: I'm talking about American fans and American critics.
To those who loved this world...
and knew friendly company therein...
this Reunion is for you.