The Deep Character System is Divine Frequency's central choice, and it is not a cosmetic class select. Three archetypes are available, each with its own weapon modification path, and the game is tuned so that different builds experience different difficulty curves. Picking the wrong one is not fatal - but it is more consequential than it looks.
Each archetype defines how you move, how you handle ammunition and psionic energy, and how your weapon modifications branch. The modification paths are where the divergence becomes real - the tree you are offered depends on your archetype, so two players at the same stage of the game can be working toward materially different endings of the same weapon.
The broad split runs between an archetype built around pressure and one built around control. The aggressive option wins fights faster but leaves you with thinner margins against the enemies the game sends in numbers. The controlled option trades tempo for consistency, which matters disproportionately in a game where enemies appear in spaces too tight to retreat from.
Which one you want depends on whether you are comfortable being aggressive in a game whose real difficulty is resource management, or whether you prefer the slower route that lets you stay solvent through a long run.
If you are picking up the free demo first, the archetype is worth trying in more than one form before you commit to an Early Access run. Because the modification trees differ, an archetype that feels weak in the first ten minutes can be the strong one later - and the reverse also holds. The demo is long enough to give a fair impression of the early tree, and short enough that experimenting costs nothing.
Not substantially, as far as the current Early Access build goes. The narrative path is the same regardless of archetype, so the choice is about how you experience it rather than what you encounter. Some dialogue and environmental details vary, but nothing in the story branches on your selection.