Actually, the specific track associated with the Prelude levels (including 0-1) is composed by Keygen Church (aka HeavenlyPele). But often, when players talk about the "0-1 Ultrakill song," they are referencing the frantic, church-organ-infused metal that plays during the combat encounters.
The environmental storytelling is subtle but potent. Scattered throughout 0-1 are the corpses of other "visitors" — humans in tattered uniforms, impaled on spikes. One audio log (found in a hidden alcove) whispers: "The machines don't want our souls. They want our blood. The blood is the fuel." This tells the player that V1, the protagonist, is not a hero. It is a vampire in metal. 0-1 does not ask you to save anyone. It asks you to consume. 0-1 ultrakill
The level design of 0-1 is deceptively simple. It consists of gray stone corridors, open courtyards, and gothic architecture drenched in a crimson glow. There are no complex puzzles here; the puzzle is the combat itself. It forces the player to learn the core loop immediately: Shoot, dash, punch, heal. If you stand still in 0-1, even on the easiest difficulty, you die. Actually, the specific track associated with the Prelude