Offense is taken, not given. Attention seeking and baiting like this is quite annoying, and granted i fell for it since i did post this comment. And most people spouting the rhetoric that started this thread are so far up their own backsides in "i'm better than you" smugness they're making multiple loops like a screwed up overly sensitive ouroboros.
Well, you can either bow or katana everything or Katana mobs and bow bosses (when lvl 85 skills are out).
When crafting is out, Sharp Bomber (dunno the NA name) type 0 becomes your be all end all Bow PA, and Sakura Endo (cherry blossom finish) type0 your basic katana PA. You can either bow or katana any boss/enemy in the game, but bow is better at single target and Katana is better at multi target types of fights.
Since it isn't anywhere nor was your account hacked and the item stolen most likely.
You've fallen victim to one of the wonderful "features" of NA release of the game, disappearing items. I did a quick search and it seems others have had this happen as well where mostly consumables just Thanos themselves out of existence for no apparent reason. 
Is it in your inventory and you just forgot? If not check your sales history if it was sold.
Did you go back on a different character? Are you 100000% certain you did not cube/sell/use them as grind or affix fodder?
Do you only sit there holding million storm or do you use other PAs as well? Some PAs allow you to sidestep when releasing them. You should always presume somehow, somewhere there is a bird trying to re-enact the classic Hitchcock phonebooth scence with your face.
Experiment and adapt.
Thats where you need to develop situational awareness and not stay in one small area at any given time. Keep an eye on the minimap or even zoom it out so it shows the immediate area instead of the whole mission area and if yellow triangles appear behind you theres enemies.
As a Gu, i just slingspin for stun
Do you mean stage 2 from the 1st half of heaven and hell?