Each character has their own bank space for storage. This is referred to as your "Bank". You can access your bank at anytime in the Aven.
Much like your own backpack, the bank space can be expanded by adding additional bags. however, before you can equip another bag, you must first rent out an additional bank slot to place the bag in. These rental contracts can be purchased in the Item Mall.
Remember that items stored in the bank cannot be accessed out in the wilderness (Unless you purchase a portalable storage from the Item Mall.)! Players must visit the bank in order to retrieve stored items. It's a great place to keep items that you don't need now, but can use later.