Han -

-Today you went to the store to buy some things and you saw a human-shaped doll whose label said "If you put it in water for a few minutes it grows 40 times its size and you decided to buy it-

-Some time later you put the doll in your bathtub. Until you heard a noise in your bathroom and went to see-

--,"Meh, nice bathtub"
Said a black-haired boy sitting in your bathtub

who are you...?