Taishokkan was bestowed to only meritorious vassals who accomplished great achievements to the Imperial Court since it was placed at a higher cap rank than Murasaki no koburi; Murasaki no koburi had been worn by Oomi (a highest officer in national politics of the Yamato dynasty) and had not been included in the Kan I junikai, but was then demoted to the fifth or sixth from the top.
冠位十二階に組み込まれていなかった、大臣（おおおみ）が身につけていた紫冠が上から5,6番目に置かれ、さらにその上に置かれた冠位の為、朝廷に非常に大きな功績があった功臣のみに送られる冠位であった。