(Basically rantaro gave korekiyo this piece of gum so yeah, and rantaro being the amnesiac dumbass he is, he forgot the gum had FUCKING SIDE-EFFECTS) korekiyo woke up when the morning announcement from monokuma appeared, he kinda forgot about the gum rantaro gave him, so he took his mask off, put the gum in his mouth and began chewing as he got up and went the cafeteria, he couldn't help but feel... a little full after a minute or two, kirumi served the food to everyone and they began eating, korekiyo's eating got a little slower and slower as time went on, to the point he was kinda not eating (probably because of that 'increasing fullness' he didn't know that the gum had.. side-effects), and the others took notice of korekiyo slowing down his eating

shuichi: "kiyo? Are you okay? I kinda noticed your eating was getting slow."

korekiyo (trying to get up from his seat, his butt jiggling as he's doing so): "oh.. I've just been getting, more and more full for some reason, it might be a gut feeling or something.. and.. now that i think about it, my kimono is feeling pretty tight. Like it's pressing against my body.. I'm starting to feel like i can barely move due to how.. heavy I'm feeling.. mmh..~ o-oh.. hic!~ urp!~"

kirumi: "hm.. how long have you been feeling like this?"

kokichi (pokes korekiyo's now slightly chubby stomach): "hm.. you're gettin' a lil pudgy there kork~"

korekiyo: "don't.. urp!~ poke me l-like that.. especially gulp t-there.. it's m-making me- hic!~ oh dear.. mmgh.. it's t-too too heavy.. i can't g-get up.."