You can also BARROW the game on your sub account by befriending someone that bought the game then request to barrow it and if they approve you can use play their game when they are not playing it for your sub account. That is what I usually do with my 3-4 steam accounts with a sub account being my storage account and the 2nd and the one I bought the game itself for the 2nd time as my main 2nd account that I will try a NG+ like run for HA much later on my other playlist with -10 videos.

For this you need 2 steam accounts with 2 pcs (or maybe a PC and Laptop[Never tried the game on a laptop]) with 2 different accounts with the game bought (bought my 2 when it was 75% off so it's like I bought it when it was 50% off)

1. Now for your main save (usually folder 00 in your save game folder) create a new save in the actual game (Folder 01[If you want to duplicate the item multiple times create a save for all available slots which will be named 02-05]).
2. Then exit the game and make a copy folder of your main file (should be named 00-copy when created) then delete folder 01 and rename the copy to 01[For more than 1 Duplication copy 1-4 more main saves then rename those to 02-05]).
3. Next, Make your 1st save on the sub-steam account with the game and speed through the game tutorial until you pass Strea's 1st In-game movie which should unlock the Multiplayer.
4. Now create a party on MP Online with your sub/backup main account save 01 before having your sub-account join it and trade away the weapon you want to duplicate to it.
5. Finally end Party and switch to your main account as the host (to be safe and avoid the Exclusive Armors and Implement Cons and any other possible MP Online Glitches), and have the sub-account join it and trade away the weapon traded to it before back to your main account leading the main account to have 2 of the same weapons on one bag slot (Which will save space in the inventory, especially for Dual Wield and weapon and/or, armors and necks you wish to gift to other NPCs or Party members like Vit weapons to increase their survivability.)

Like what I did from this video's 8:50 time stamp that shows this trick in action.

Odysee/LBRY Original File without youtube changes and on the full game playlist
https://odysee.com/@CVGamerLBRY:6/ZDC-NA-SAO-RE-HF-%E3%82%BD%E3%83%BC%E3%83%89%E3%82%A2%E3%83%BC%E3%83%88%E3%83%BB%E3%82%AA%E3%83%B3%E3%83%A9%E3%82%A4%E3%83%B3-%EF%BC%8D%E3%83%9B%E3%83%AD%E3%82%A6%E3%83%BB%E3%83%95%E3%83%A9%E3%82%B0%E3%83%A1%E3%83%B3%E3%83%88%EF%BC%8D-PC-Part-259-Final-Advance-Dragon-Boss-Low-Level-Victory%2C-MP-Online-Duplicating-and-Enhancing-to-4-%2B15-plus-Leaf-and-Kibaou-Weapon-Upgrade-Gift:9?r=5fCnAhvZcUwaFeWjuiaajepZ8xhjrkQh

Youtube on the almost full game playlist
https://www.youtube.com/watch?v=ravVyoDp_-Q&list=PL-_EX_vMMS5pLfdLkGTa7EyOl9w97LYU7&index=257&t=530s

With this duplication Trick, you will make this Grindy game a LOT less Grindy as you will probably only need to grind a few items like the Last Attack Equipment from 2 HNM DLC Bosses as well as other DLC items and some other items are not tradable, and of course, you will still need to grind a lot for the MANY other Sword Mastery Stars. (Max 3 which seems to need 10k separate uses to get for increased damage on the SS?)

Hope many find this guide helpful.