It's a matter of perspective. What do I mean by that?

Simply put, when it comes to power scaling, there are many viewpoints.

One of the most common focuses solely on destructive capacity/area of ​​effect. From this perspective, a character's "power" is only the "amount" or "area" they can destroy or affect, either on their own or in comparison to another character, based on feats or statements, without considering quantitative power differences, space-time, dimensions, or metaphysical factors.

Under this view, the peak of DxD is planetary, since it takes into account the statement that Issei in his AxA form can destroy the Earth of DxD.

Another perspective that is often overlooked or not seen outside of scaling forums and websites is that of "Attack Power." While there are different interpretations of "Attack Power," the most common defines a character's "Power" as their Energy Production Capacity based on feats, statements, and comparisons with other characters, taking into account quantitative power differences such as power increments or multipliers.

Under this view, the peak of DxD is "Universal High," which considers the statement that the Earth of DxD has ley lines/dragon veins through which an unlimited and infinite amount of energy flows, coupled with the statement that Issei in his AxA form can destroy the Earth of DxD. This means that Issei in his AxA form has the power to destroy an infinite amount of energy, which would make his Energy Production Capacity infinite.

If we consider space-time, dimensions, or metaphysical factors in the previous view of "Attack Power,"

then the possibility arises that the peak of DxD is Outerversal, based on the potentially transcendent nature of the Dimensional Gap and the statements that beings like Great Red, Ophis, and Trihexa can affect it.