This a Moonmelon, scientifically knows as asidus. This fruit grows in some parts of Japan, and is known for its vibrant blue color. What you probably don’t know about this fruit is that it can switch flavors after you eat it. Everything sour will taste sweet, everything salty will taste bitter, and it gives water a strong orange-like taste. It's also very expensive...costing about ￥16000 JPY (which is about 200 dollars).
Dr. Oz: "Peanut Butter & Chocolate--This tasty duo will satisfy even the most voracious sweet tooth. Melt a bar of dark chocolate and mix it into a jar of organic peanut butter. Leave it in the fridge so that it cools and the flavors blend. When a sugar craving strikes, have a spoon. One spoonful has 4.5 grams of sugar. Compare this to your average brownie with a whopping 30 grams of sugar, & you’re well on your way to shaking your sugar habit in healthy ways you never thought possible!"