Reach weapons and opportunity attacks

[K1]

How does that work?

Imagine a 2 characters adiacent.
1 wants to move away from the other.

If you strike, you Trigger a reaction.

If you step, you have to do it twice? Or the reach property just works on during a character turn?

They seem too good since they allow you to Cover more space, and eventually not to waste actions in movement like steps or strides.

If you also are a fighter, or have that dedication, you will be able to reach 15feet with a lunge.

[Fuzzy-Wuzzy]

If the weapon has the reach trait, its reach is always 'on', not just during the wielder's turn. So yes, you have to Step twice to get away from a fighter wielding a reach weapon w/o triggering their AoO.

Covering more space for AoO and similar reactions is one of the main reasons reach is a big deal. (Of course, most combatants don't have AoO to use it with.)

The fighter's Lunge won't help by itself, since that doesn't work outside the wielder's turn, being an action. The 12th-level feat Lunging Stance that it leads to will let an actual fighter do a lunging AoO.

[BellyBeard]

Yep, if you have reach it's good to be adjacent if they plan to move away (they will most likely take the AoO rather than waste their whole turn moving away from you), or to be one square away if they plan to melee attack you so they have to step to get to you, wasting a third action.

Reaction builds are good, and most people recommend reach fighter as one of the highest and most consistent damage builds.