Three modes, and you are not locked in
Story, Normal and Hard. You can change between them at any point in a playthrough, and switching does not reduce the rewards you get. Story Mode softens parry timing and enemy damage for players who are here for the narrative — and because rewards are unaffected, taking it is not a compromise on what you unlock.
Story Mode widens the parry window rather than removing it
This is the distinction worth having. In most games a story difficulty just drains enemy health, which teaches a player nothing and leaves them helpless if they ever switch up. Here the softening is applied to the parry timing window itself and to the damage you take, so you are still practising the mechanic the harder modes are built on — the same parry, with more room. That is why taking Story Mode early and moving off it later works, and why draining health bars would not have.
What this means in practice
Play more aggressively than the genre trains you to. FP only comes from parries, so a cautious player is a starved one, and the mode you pick changes how much room that parry has rather than how hard the enemies hit. The other half of the aggression argument is what a death actually costs you, and that is deliberately not answered here — it is a different question, its evidence is weaker than anything on this page, and one creator disputes a line of it. It has its own page for exactly those reasons.