Irish mobster oc x dxd

Sean Mason was the boyfriend of one Rias Gremory but he had a hidden secret that he didn't tell anybody but those who worked for him he is one of the mafia bosses of the Irish mob he was over in Japan working on a deal with the yakuza. When he caught the woman he loved in bed with a pervert.
what's going to happen when the supernatural word we are used to encounters its mafia.