User blog comment:B214/Volume 21 info & spoilers/@comment-199.216.41.253-20160419203901/@comment-26345952-20160420012654

Well DxD form is the power of Ophis for the most part, but Great Red does take in part as Issei's body is made his flesh and makes Issei handle Ophis power for a short time.

Technically yes, this is mostly taking the power of Ophis and awake it, Great Red is more of a support for it to happen, but Issei is yet to use Great Red powers (other than dragonify some parts of his body).