I’ve thought the idea about making it pony style cuz I watch mlp, and then I said “let’s give it try”.
3 Reasons why I made Rias an alicorn:
Both a devil and an alicorn can live for a long period of time, let’s say a thousand years. (Afterall, Rias is a pure-blooded devil)
She is mentioned as the “Switch Princess” of the Oppai Dragon Show.
She would be a beautiful princess to Issei and he could be her knight and shining armor except Issei is her pawn but hey… he’ll do anything to protect Rias.
As for Issei, eventhough he is the Red Dragon Emperor, I just made into a pegasus, no reasons.