Collect Maimais to unlock item upgrades for 9 of your purchased items, and the Great Spin, a special, ultra-powerful Spin Attack.

Great Spin - Master Sword/100 Maimais
Nice Bomb - Bomb/10 Maimais
Nice Boomerang - Boomerang/10 Maimais
Nice Bow - Bow/10 Maimais
Nice Fire Rod - Fire Rod/10 Maimais
Nice Hammer - Hammer/10 Maimais
Nice Hookshot - Hookshot/10 Maimais
Nice Ice Rod - Ice Rod/10 Maimais
Nice Tornado Rod - Tornado Rod/10 Maimais