User blog comment:Crimson and Darkness/Shin DxD 3 discussion/@comment-3965848-20190811085546/@comment-25262334-20190811134908

I don't think that Kunou will be seen as sister to Yasaka's children with Issei once Kunou will be have his children herself. Most logical conclusion is that both raise their children as siblings and will not too much mention own relation between them.