[Rias]

Spoiler for s;g true end spoiler... just in case?:

The trailer does state that it's the continuation from the beta world line, after Okabe went back to July 28 (the first time) but failed to save Kurisu. So it basically chopped off the 2nd half of the True End, and went from there. Which probably explains future Okabe from your picture. To add onto that,

Spoiler for In one of the drama CD...:

Future beta line Mayushi calls her earlier self, during the gap between Okabe going back in the time machine the first and second time, to make sure Mayushi cheers Okabe on when he returns, as she knew that Okabe was going to fail the first time.

I heard Epigraph has been out of print for a long time, so it wouldn't be a bad thing if they reprinted that because of this