Calories is a type of stat that will change the form of Hilda.
To gain or lose calories, Hilda must use her Calorie Drain skill on enemies; Depending on the enemy she will either gain, or lose calories.
The stat is represented in a bar and goes from -100 to 100.
If the bar is between -99 to-11, Hilda will be in her Slim Form. If the bar is -10 to 10, she will be in her Pink Bat form, and finally, if the bar is +11 to +99, she will be in her Curvy Form.
If it goes to +100 or -100, her stats will go really high and she will go into mask form (Slim Mask or Curvy Mask, depending on the + or -) for only 3 battles, before turning into Pink bat with 0 calories.