It looks like Kirby has eaten a lot recently, so he became fat in our fanart Kirby Thick Sticker. Consuming more calories than the body needs regularly can lead to weight gain and an increase in body size. Eating a diet high in calories, unhealthy fats, sugars, and processed foods can contribute to weight gain. Even more, Kirby didn't have physical activity lately and had a sedentary lifestyle, which led him to gain much weight.