Opening: Devil Fruit can be upgraded

Story of: Opening: Devil Fruit can be upgradedRebirth in Shimotsuki Village, obtain the devil fruit upgrade systemYou start with a cold fruit, and your defective abilities all depend on upgrading.Upgrade once, no longer afraid of sea waterUpgraded twice, frozen fruit is readyUpgraded three times, the snow fruit is readyUpgraded four times...Frozen fruit is readyUpgraded five times... reached the limit, can't upgrade anymoreThen let's merge...