Your options for unlocking are:

-Getting a 99 WOE weapon the olde way (involves killing bunch of NMs etc but you need less dice/residue/coins)
-Getting a 99 WOE weapon using the -1 weapon (involves 30 coins, 100 devious dice, 100 liminal residue) EASIEST
-Getting an empy to 90

In all cases you need to have unlocked Jueno Tier Voidwatch in order to unlock.