In NiOh 2, you have access to item shortcuts. This page has information on how to assign them.
You can assign item shortcuts in two ways. The first is to enter the inventory menu. There you can select the item you want to assign. Confirm and click on the "Set as shortcut" option and select the button that will correspond to this item.
The second option is to go to the inventory menu. There you can enter the shortcuts menu, where you can choose which item you want to assign to a specific button.
By default, shortcuts are assigned to the d-pad, so you can have four of them active at any given time. However, you can create yourself several different sets that you can switch between (you can have a minimum of two and a maximum of four). You can make changes in the settings menu.