Ryufu said:
I thank you for the answers. One other thing though, do you have to actually do damage to trigger the weakness? I am a bit worried cause I might miss with some of the less leveled up weapons I have
All true elemental WS cannot miss and will proc even if they do zero damage. Certain effects, such as Ningishzida's Pyric Bulwark, will cause them to have no effect, but other than that they'll always land, even if your accuracy is terrible.
Tachi: Jinpu and Tachi: Koki are hybrids, as they have elemental properties and can give amber light when they're used to kill mobs, but they can miss and are affected by Sneak Attack.