The platycephalid genus Onigocia Jordan and Thompson, 1913, defined by, e.g. pored lateral line scales numbering about 40 or fewer and the infraorbital ridge finely serrated, presently includes the following nine valid species at present: Onigocia bimaculata Knapp, Imamura and Sakashita, 2000, Onigocia grandisquama (Regan, 1908), Onigocia macrocephala (Weber, 1913), Onigocia macrolepis (Bleeker, 1854), Onigocia oligolepis (Regan, 1908), Onigocia lacrimalis Imamura and Knapp, 2009, Onigocia pedimacula (Regan, 1908), Onigocia sibogae Imamura, 2011 and Onigocia spinosa (Temmink and Schlegel, 1843). Of them, only O. bimaculata, O. macrolepis and O. spinosa have been formally recorded from Japanese waters. However, a single specimen of Onigocia [70.6 mm in standard length (SL)] collected from Mugi-oshima Island, Tokushima Prefecture, Japan in 1994, was recently found to be identical with O. grandisquama, being characterized by I + VII-11 dorsal-fin rays, 11 anal-fin rays, 12 pectoral-fin rays, 10 caudal-fin rays, 34 pored lateral-line scales, no small spines on the lachrymal ridges, 2 preocular spines, 9 pterotic spines, a single ocular flap not attaining to the posterior margin of the orbit, small papillae absent on the eye, the upper iris lappet short and branched, a notch absent on the suborbital ridge below the eye and interopercular flap, and a head length 48.6% SL. Although the latter has been widely recorded in the Indo-West Pacific, it has not been previously reported from Japanese waters; thus, the specimen represents the first record of O. grandisquama from Japan, as well as the northernmost record of the species. The Japanese specimen is described in full and a new Japanese standard name (Nameraonigochi) is proposed for the species.