Dual kingship was a model of rulership practised by a great number of societies and cultures, namely, by the Sarmatians (Scott Littleton), Turkic eg Khazaria, Scottish, Hungarian and Scythian(Susan Tomory), Spartan(Sahlins), Indo-Greek and Indian rulers, also among the Romans, Germanic and Dacian tribes, as well as possibly among the Huns(Otto Maenchen-Helfen and also Paivi Kuosmanen) The Twin Brothers or Rival Quarreling Brothers myths can usually be found in narrated or written clan genealogies and/or court epics and songs.
The brother motif appears as well (Hoderi-Hoori brothers) in the earliest chronicles of the royal genealogies, but now a new paper concludes that the dual kingship or diarchy model of rulership can be inferred from a scrutiny of the artefacts and layout of the Kofun Period tumuli of the 3rd to 5th centuries. See the explanatory note of the paper below:
Dual Kingship in the Kofun Period as Seen from the Keyhole Tombs, Urban Scope Journal – Volume 4, May 2013 by Naofumi KISHIMOTO
Dual Kingship in the Kofun Period as Seen from the Keyhole Tombs
“Heralding the beginning of Japan’s state formation, the Kofun period (3rd-6th century) witnessed the emergence of a supraregional consolidation of the Japanese archipelago superseding that of the preceding Yayoi period. The enormous number of tombs spread across the archipelago palpably limns the relationship between local chieftains and the paramount Wa kings. For four hundred years, this relationship was characterized by the construction of monumental kingly tombs commissioned by the Wa elite and the building of smaller-scale iterations by local rulers.
A diachronic analysis of keyhole tomb (zenpōkōenfun) construction in the Kinki region of central Japan suggests the coexistence of two disparate lines of tombs adopting separate blueprints. A clear reason for this, however, has yet to be proposed. I have come to view the nature of Kofun-period rulership as divided between two kings: one orchestrating state ritual and the other managing administrative affairs. This view, known as “sacred-secular dual kingship,” has long been espoused by historians of Japan’s early texts. Even from an archaeological perspective, the tombs of the incipient Ōyamato Tomb Group suggest the coexistence of two different types of kings. Arguments for “sacred-secular dual kingship,” however, have focused on a gendered division of labor between male and female paramounts, while nevertheless adhering to the image of a monolithic imperial line of male administrative emperors, informed by Japan’s earliest domestic histories, the Kojiki (712) and Nihon shoki (720). In this paper, however, I propose a politico-ritual model of dual kingship in which two coexisting male kings assumed different leadership roles; furthermore, I suggest that even the role of the sacred king (often framed as a shamanistic queen) had been filled by a male from early on. There were thus two nuclei of authority in the Kofun period. Before unifying into a single line in the early-6th century, however, this structure was responsible for political instability and regime changes.”
This is a streamlined version, prepared for English translation, of an article originally appearing in volume 208 of Historia (2008). Read more of the paper here.