Callanthias japonicus has a dorsal fin which is supported by 10 spines and between 11 or 12 soft rays while the anal fin has 3 spines and 10 or 11 soft rays. It has an elongate, compressed body with a short, blunt snout. The preoperculum is rounded and has no spines or serrations but the operculum has 2 spines. The overall colour is pink, shading to yellow on the blower body. This species has a maximum published standard length of.
Callanthias japonicus is found in the northwestern Pacific Ocean where it is found from southern Japan, southern South Korea south through the Ryukyu Islands to Taiwan. It has been claimed from the Emperor Seamounts but this has to be verified. This species is found over rocky reefs at depths greater than. It feeds on zooplankton and frequently forms mixed schools with anthiinserranids.