The designs of Rias and Akeno are really good but I think that it was not necessary to use them for NTR especially with the stupid "friends" of Issei when they could have been used to represent a moment IsseixAkeno and IsseixRias, and I know that more than one would tell me: "But I like the NTR "and in response I just say that I don't like the NTR instead :3