I'm guessing it's actually more of an "alternate route" vision, considering it looks like Redyue reversed the situation, with Kouta becoming Byakko Inves while Yuuya becomes Gaim.
She is showing Kouta what will happen from the start until the end, if Kouta becomes an Inves since the start.
Not sure why Redyue shows that to Kouta, though. Needs to see the sub for the preview or even the episode to find out why.