User blog comment:B214/Question and Answers 4/@comment-24098614-20141011224426/@comment-24098614-20141012025909

Issei might be have a Dragonic heritage in his body but I think that he does have the same weakness as any Devils so he should avoid any Holy Swords or that Sacred Gear that attacked Saiaorg that left him in such a horrible state because when he put those Evil Pieces back in his body he inherited the weakness towards Light.

The Sacred Gear that I fear more for any Devil to me is the True Longinus that Cao Cao has nobody can withstand the stab of the spear specially Issei since he is part Devil.