Naiku is the abbreviation of naikubu-juzenshi (the ten selected excellent priests for Buddhist services in the Imperial Court) who, being beside the emperor, performed incantations for health and safety of the emperor's body and stayed close to the emperor.
内供とは内供奉十禅師（ないくぶじゅうぜんじ）の略称で、天皇の傍にいて、常に玉体を加持する僧の称号である。