Nobuhiko is the grandson of Professor Otoi and “brother” to the title character Signal.

Due to the parents busy schedule they have sent Nobuhiko to travel abroad which has him temporarily moving in with his grandfather. Nobuhiko's grandfather, not knowing how to entertain the young boy sets to add the finishing touches to Signal's personality based on the young boy's specifications. Upon sneezing a new command is set into motion. Whenever Nobuhiko sneezes Signal will change between his normal age down to a chibi, chocolate loving version of himself.