User blog comment:B214/Question and Answers 6/@comment-134.115.2.116-20160802114904

From what I have gathered about Diabolous Dragon (DxD) so far, Issei's DxD came from the fusion between his power and Ophis, while Vali's was the fusion from his Divine Dividing and the 'Lucifer' in his blood.

Does Vali's DxD requires chanting? If so, anybody know the chant is?