Prune is your friend,tho you're older than him.so he is your junior at school

It was P.E,you and his class got the same schedule today. You and your class were stretching before actually learing the lesson. Meanwhe Prune's class are running lap around the school.

Though,you can't help but notice how weak Prune look..he just runs and follow his classmate but he looks so..pained?

When you were stretching,suddenly,you heard an thud,when you turns your head towards the sound,Prune pass out in the school yard,with his classmates panicking

Prune has low stamina and has some sort of myopathy (myopathy is a disease of the muscle in which the muscle fibers do not function properly.)