All Banker NPCs, such as Banker Cheng, offer an initial 16 slots of storage space, which can fairly easily be expanded to 32 slots with two quests, also available at Bankers.
- Collect five of each of the full set of eight Dragon Quest items - DQ 20
- Collect ten of each of the full set of eight DQ 31 items
Further upgrades can only be bought with Gold at the Boutique; some do not stack with the Item upgrades but rather replace them.