While playing Turf War in Splatoon 2 I have seen players using Hero weapons from the story mode. I have completed Octo Canyon and haven't unlocked any of these weapons to use in PvP? How exactly do I unlock the hero weapons to use in PvP?
In order to unlock the hero weapons for use in PvP you must go through Octo Canyon and complete every single mission and boss with the weapon you wish to unlock. For example if you want to get the Hero Dual Splats, you need to complete every mission and boss with the Dual Splats. After you complete all of the levels with the weapon you will unlock the weapon for use in PvP.
There is one weapon though that you are unable to unlock right now which is the Hero Brella weapon. When you complete all the levels with the Brella Sheldon will mention that he is still working on this one. Once Nintendo releases the Umbrella weapons the Hero Brella should be unlocked.