The Monster With 21 Faces

Haru gets two bottles of the drink, one for free when he gets it from the vending machine. He drinks one bottle and then starts on the other. But before he can finish that second bottle, he begins to feel sick. His symptoms are acute, intense, and they're getting worse fast. The next night he stops breathing and he ultimately dies from his mysterious illness. Test later revealed that Haru died from paraquat poisoning.