So what I find interesting is the last Demon King handled by Mephisto was considered 'Kind'
Further, his last lord wanted to do it all over again, and was a member of the Many-Eared race
Im wondering if Iruma's kindness is what interested him in the first place, or if the two of them have very different definitions of 'Kindness', but also, if this is all a sort of penance to the fall in stature of the Many-Eared race, as Mehpisto likely turned his back to his responsibilities while he wallowed, feeling like his purpose was gone.