To unlock the ability to buy the following characters for 10 Medals, beat each attraction (excluding the Bomber Houses) in each zone twice to get the Card and Medal. A "Special" option will become unlocked in the Information Centers where you can purchase the characters:
CHARACTER - ZONE Ao-bon (Blue Bomber) - Spade Zone Gold Bomber - Diamond Zone Kuro-bon (Black Bomber) - Castle Midori-bon (Green Bomber) - Club Zone Pretty Bomber - Heart Zone
After failing to complete a mini-game numerous times, it will eventually ask you if would like help in exchange for one Token. Double tap the icon between the "Yes" and "No" options to make the mini-game much easier.