I finally drew Asher's sword design
The final version, the one that makes sense. Meaning I am probably redrawing Asher to fit this new design at some point.
The sheathe slides up to create the back of the greatsword blade. The trigger is done by hitting the switch on the katana while unsheathing it, automatically it should get stuck in a partial draw at the same time as forming the giant blade. What holding the switch does is it unhinges the second half of the sheathe, and pulling the katana out drags the sheathe into its new locking position to form the greatsword.