I’m a dumb foreigner but I’m still going to try and look at this symbolism. Anyway I did a little research on the “Torii” gates Kaneki is trying to swim through to escape to the outside world. Apparently the are used in the Shinto religion to mark a passage between somewhere worldly or “profane” to sacred place. Which is why they’re often seen at Shinto shines (I’m no expert though so please don’t crucify me).
The flags (as kurosuzumenihongo informed me on a previous post I made) around the “Torii” seem to have Kaneki Kaneki’s name written on them in old script. Most likely to represent all the people calling back. (Additionally there’s some difficult to see writing on the signs which seems to say “Payment” and “service”).
But the meaning behind Rize asking “Where are you going? murderer.” is fairly o obviously her asking why he thinks he deserves to pass into the sacred place through the gates (reality).
And seeing as Kaneki was also seemingly forced to face his dead before he could keep moving… I think it’s likely this imaginary Rize like in the past with Jason, will be the the guide that makes him face his profane actions and reasons before he can “pass through” the gates to the “sacred” reality
He’ll be forced again to come up with a conclusion why he did the things he did. And will then have to find the reason he can give as to why he should be able allowed. He knows this Rize is him now so he’ll have face his own feeling that he doesn’t deserve to live
I might write more on this later when I’ve collected more information.