PopHappiness - Popハッピネス  Suggested by jkrosado 

Most likely proprietary.

Made by the same designer as Pop Joy, the font used on Paper Mario TTYD and above. One of Kirby series (Return to Dream Land) also used this. It's also called Pop, but I forgot the last name

It's not proprietary. It's made by Fontworks Japan, Inc. and it's called FOT-PopHappinessSTD.