Brilliant King appears on the 7th and 8th Path of Yomotsu Hirasaka within the Midnight Channel. It will attempt to use its Judgement skill and will also summon a Reckoning Dice to the field. After being defeated, it may drop a Silver String. Selling 10 Silver Strings at the TV extension of Daidara will unlock the Haten Robe female armor.
In Persona 4 Golden, the Brilliant King appears in Paths 6 and 7 of Yomotsu Hirasaka. It has additional skills than its counterpart in Persona 4, as well as able to summon various enemies such as Gracious Cupid, Rampage Drive, Ptarmigan Panzer, Berserk Turret, Successful Juncey as well as the Reckoning Dice.