Dainichi Nyorai is a Buddha in the context of Esoteric Buddhism, which includes practices that utilize mantras to attain enlightenment. The mantra chanted in veneration of Dainichi Nyorai is: "Oṃ vajra-dhātu vaṃ" ("金剛") and "Oṃ a vi ra hūṃ khāṃ" ("胎蔵"). In Esoteric Buddhism, Dainichi Nyorai represents the truth of the universe, and also is a reference to the universe itself. Dainichi Nyorai has two aspects, "金剛" and "胎蔵". "金剛" means diamond, and represents the wisdom necessary to attain enlightenment while "胎蔵" represents compassion. These two aspects are represented differently in the Dainchi Nyorai statues by the way its hands are posed. This statue in the picture represents the first aspect, "金剛". Fudo Myoo is an incarnation of Dainichi Nyorai, or the representation of Dainichi Nyorai's inner will.
This statue is "眼入", meaning that it has glass eyes painted with pupils inserted. The insertion of transparent eyes into Buddhist statues is a uniquely Japanese technique. One remarkable point of this technique is that when you look at this statue, your eyes will still match the eyes of the Buddha from any angle. Many people believe that this helps you appreciate the connection you have with the Buddha.