This is a series I need to find time to rewatch as it has a constant dark presence over your typical quiet hero protagonist. It is similar to Berserk as far as personality and the theme it aims for. From the creators of Trigun I can see their style in some of the concept design. A worthwhile series that stands well on its own separate from Trigun.
Brandon Heat and his friend Harry are orphans on the streets surviving by thieving and other means. They soon gain the attention of high rise gangsters and gradually move up the chain of command. Throughout the series we see their friendship tested and evolve to become something neither of them truly saw coming. Betrayal is the main theme, but the series also includes survival through gaining power and the question of how long before it finally corrupts.
The monsters in this series make me think of Resident Evil, so if you want more like that with a somewhat different style and back story then enjoy.