Haki was obtainable from buying a Haki Gamepass. This game pass would then randomly give you 1 of 3 types of haki. Rarely a player could have two kinds of haki. Currently haki is no longer obtainable, but still in-game for those who already got it.
Types of Haki
Haki had in-game abilities that granted players new skills.
When health was low (around less than 50%) the player's Right Arm would turn to a dark silvery grey. This arm would also turn any holdable weapon (swords and pistols) the same greyish silver. This grey could harm all players including logia players. No extra damage is given to the sword, but the Right Arm does it's own damage.
You can attack Logias of all kinds, with any sword with no restricted amount of health. According to Aurarus, soon you may be able to see every player 250 meters away because of a gui that is over their head by toggling a button.