Hujikar Weapon drop

Do I HAVE to use keys on the chests to get any sort of weapon from this world boss? I ask this because in other boss fights (dungeon and otherwise), there used to be a sealed weapon as a drop plus other extras. Hujikar seems to drop just one chest with a weapon chest inside it. The Hujikar weapon is breakthrough material and is required for me to level up the weapon.
Follow up question if yes: Is using the survey brilliant key for this a good option? Or is there another RNG chest like this further in the game for which I need to hold on the key for.