We'll have to wait till it comes out, but it seems like they set it up such that the fake background that Cloud tell in the original is actually what actually happens in the remake. But yeah, Sephiroth is so boring in 7R, he's like a jealous ex boyfriend who can't get over that his ex is moving on so he stalks him. Its a shame because Sephiroth isn't that interesting in the original, but the game build him up really well, but all of that is deflated in the remake.
So there are two short stories written by the OG writer for FF7 called Lifestream Light and Lifestream Dark. They are meant to be stories that bridge the narrative between FF7 original and Advent Children.
Lifestream Dark tells the story of the essence of Sephiroth who still exists in the lifestream as a consciousness because of Cloud's refusal to forget about him. Cloud as we know is torn up with the guilt of Aerith's death and how he should have stopped Sephiroth. In so doing, Cloud's memories keep the lifestream from being able to completely absorb Sephiroth, his memories prevent Sephiroth from truly dying. Sephiroth realizes this and runs through the lifestream touching people, corrupting them and leaving his Stigmata upon them. Because if he can make enough people think about him, envision him he can use that to manifest himself again, through the few remnants of people with Jenova cells throughout the world.
Thus his line at the end of Advent Children "I will never be a memory".
This is also how Sephiroth cannonically chases Cloud to other universes like Kingdom Hearts and Smash Bros. Because he exists where-ever Cloud is because Cloud can't let the memory of him go.
Now assuming that the Remake saga is a technical sequel to the FF7 series (post advent children), Sephiroth appearing to fuck with Cloud fits because he needs Cloud to be thinking about him in order to continue to exist through the lifestream, (even when he's physically frozen in the northern crater). Also keep in mind that everything Sephiroth does in Remake is to try and break Cloud away from the choices he made in the original game. Everywhere Sephiroth appears, he is trying to get Cloud to do something else.
In Chapter 2 where in the original game Cloud meets Aerith for a minute and they break away, Sephiroth appears and leads Cloud down a bunch of alleys to try and prevent this meeting from happening. If Cloud never meets Aerith then there is no reason Cloud would get invested in the big Shinra hunt nor the chase for Sephiroth himself. Nor could Cloud follow Aerith to the Temple of the Ancients to interfere with getting the Black Materia. Basically a lot of shit changes if CLoud never meets Aerith.
But what happens, when we see Aerith she is fighting away the invisible ghosts because the planet NEEDS her to meet Cloud, so the ghosts keep her in town only enough for her and Cloud to meet, but when the meeting goes on too long they appear again to chase her away.
The story of Lifestream Light is in the same way Sephiroth's essence remains whole within the lifestream, Aerith uses her communication with the planet to keep herself together in the lifestream as well. She helps keep Holy at the ready to unleash it for the planet as soon as the Sephiroth's hold breaks, she watches the party but mostly she watches Sephiroth. When he finally dies and becomes part of the Lifestream she follows him, tracks him, and watches what he does while doing the best she can to minimize the effects of his geostigma.
This leads to Remake where throughout the game Aerith says and hints at things that she should have zero knowledge about. People speculate that this is because the original Aerith is feeding the Remake's Aerith hints about what's going on, what will happen, and how things need to happen. Giving her knowledge and abilities she should not have at this point in our story. Much in the same way the Sephiroth essence is trying to fuck with the story, Aerith's essence is trying to save it.
Kitase has said that the original ending of FF7 is the bad ending. We see Red13 running through a canyon to Midgar which is revealed to be completely overgrown and reclaimed by nature. This is a world without humans, who've all been killed off by the planet's weapons to prevent humans from continuing to drain Mako energy or abuse it's resources ever again. This is the bad ending so to speak and through the Remake's upcoming events it's hinted that there is a possibility that this time we can make a better ending happen for everyone.
