Sub class questions

*Do you get to use your sub class weapons? Say i pick gunner and my sub class is fighter. Do i get to use the Katana? If not what do we get from a sub class?

There are certain weapons that can be used by more than just their original class, it's also possible to add another class to a weapon using a rare item from the AC scratch and customizing it in your room, but I recall that being a terrible idea due to weapon customizations messing with the crit rates.