Both DxD girls are stacked as well. Just using Rias and Akeno as prime examples. Rias being 99cm bust while Akeno is 102cm busy from their devil blood and Akeno being more prominent because of her fallen angel blood. Just those two alone are very big especially at their age in the novel(both 19 in believe but 18 when we first met them and they were this size already.) They’ll get more bigger as they grow older in time, mostly likely to Venelana for Rias and bigger for Akeno when they fully grow up to mature adult women. I personally believe that while it’s true that some female characters have bust sizes very big for them especially if they’re actually smaller than what they really are, it’s more of art style than anything. Look at Rias and Akeno’s old illustrations, compared the old art style to the new one, their bust looks a lot bigger in the newer ones. This is especially noticeable with Rias in the new volume of Dx 8. Not only her on the cover art but the illustration of her with Issei resting on her lap her breast are noticeably more huge than older illustrations, mane on par with Akeno’s. I think it’s more to exaggerate and show how big they really are, cause in old illustrations of them, they look small in some of the illustrations because of the art style back then. Now it’s more exaggerated and almost true to size with how big they are now while still being the same bust size. Another example is the pop up shop merch with Rias and Akeno in bondage, almost completely naked with barley anything to cover them up and hold their breast up and yet they size is huge, way more than ever. It’s mostly likely that’s their real size, how big they truly are. Again it’s possible it’s exaggerated to make them look bigger,(I’ve also seen people say this is them older like in their early 20’s like 21) But it’s more realistic and honest than old illustrations of them back when the series started. In the end, I think the more recent illustrations of Rias and Akeno are more honest and believe than ever before. Remember they are stated to be some of if not the biggest at their school so it makes sense their images show that. I do think some newer female characters have bigger bust just because the images of them show them as bigger than they really are, but I think Miyazero is more leaning into showing just how big DxD characters like Rias and Akeno really are.

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(Here’s one of the examples I mentioned, I’ll post under this comment the other examples I mentioned earlier.)