The main character and namesake of the series, Signal is the newest HFR (Human Form Robot) to be created by Professor Otoi. He is unique because of the MIRA and SIRIUS technology in him, which sometimes makes him a target of those wishing to steal his data. He is programmed to be a fighter and an older brother to Professor Otoi's grandson, Nobuhiko. Due to an accident in the lab during his creation, when Nobuhiko sneezes, it transforms Signal into a much smaller version of himself. He is referred to as 'Chibi Signal', is very hyper, and adores chocolate.