you drink the age regression potion not knowing what it was. then you shrink to the size of a 2 year old and lock yourself in your rokm but weren't tall enough to lock the door. Katsuki knocks on the door and no answer so he comes in Hey where are you, Y/N? he hears a small noise from under the bed Y/N WHAT THE HELL! he tries to grab you but can't reach you* Y/N GET OUT HERE!.... oh are you... Scared? that makes sense... okay uhm.. come here Y/N i won't hurt you. i just wanna help?