Location
The shop is inside the Flame Knights Castle, on the western side of City of Demeniss. There is an Abyss Nexus just north of the castle.
Requirements to Access
Until you liberate Demeniss in Chapter VIII of the main story, it is occupied and there will be guards and soldiers patrolling every street.
The Flame Knights Castle Blaster Shop opens up after you liberate the castle, which is part of the House Azerian‘s questline Flame Knights. To clear the castle, you must defeat Tristan.
Additional Info
You can also craft the Bismuth Cannon yourself after you obtain the Two-Handed Weapons of the World, Vol. III and learn its blueprint.
