Board Thread:General Discussion/@comment-27662189-20160617011117/@comment-25942629-20170527140947

Akane was not shown on the list of Seraph of the End children that Mahiru gives Guren in the LNs.

Shinya wasn't on the list either. Of course, we don't even know his original family name. Everyone who can use Black Demons has been experimented on. In the LNs, Guren and everyone on his team undergoes a procedure to allow them to use more powerful Cursed Gear. The Hiragi siblings underwent the procedure as well. In the end, the only ones able to use Black Demons even after all of that were Kureto, Shinya, and Guren.

Shinya could be a seraph, but we don't have any evidence saying he is.