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I was thinking about this part of Trace of Two Pasts and its potential future implications:
There might come a day where she would no longer be 'the last descendant of the Cetra'.
No wonder that so many people got excited at the idea that perhaps this is an hint that Remake takes place in an alternate timeline where Aerith may survive and have kids.
Is she thinking to Cloud as a feasible partner? Maybe, I wouldn't exclude part of the intent here is to set up a future insight on Aerith's romantic feelings.
However I find this part extremely intersting for a different reason, and considering it into an overall view of the story, I'm guessing if the real intention of the writer wasn't to set part of the foundation of a greater theme of FFVII.
I think it's safe to assume that both Trace of Two Pasts and Picturing the Past, despite being purposedly written to enrich the narrative of Remake, are meant to expand the story and its characters as a whole. In other words, these two novels fit both the OG and the Remake, whether the latter is going to have a different ending or not (not going to discuss this here), nothing clashes with the original plot. No mentions of Whispers or glimpses of the future, just an insight and a modernization of the characters' backstories.
As regards the OG we already know what happens to Aerith:
In an extremely short span of time she endures a lot of internal struggles and development.
First of all she's torn between her human and Cetra sides. It's more my personal interpretation for now, but I think that Aerith tried for years to set aside her Cetra heritage. Being the last one, the special one, always turned out to be a negative thing. Her mother endured terrible experimentations that lead her to death, she had to live imprisoned and alone for years and even when she started living in Sector 5 with Elmyra she was constantly under surveillance, all this because of this uniqueness. Her special powers made her the strange one, who could hear voices and perceive people dying, and Aerith didn't want all this, she wanted to be as normal as any other girl. She wanted to work, to ejoy life, to be happy and free. But whenever her powers would have awaken again Shinra was ready to take her back to its labs. This unexpected journey forced her to learn about her heritage and accept the fact that her wish to be human couldn't overshadow her Cetra responsibility. And when she fully accepts herself, her powers and consciousness finally resurface.
Moreover she has to face her inner turmoir concerning her feelings. The boy she loved is dead, although she's unaware of the reason why he didn't come back to her 5 years before, and now she needs to understand what Cloud really means for her. He bears similarities with Zack yet he's not Zack and she perceives there's something different under his cold surface. And she finally resolves she wants to take a step forward and meet the real Cloud, wherever it may lead.
But all these quick realizations break off in the worst way possible. After more or less one week Sephiroth kills her. The White Materia falls in the waters of the Forgotten City and as far as we know it loses all its powers and becomes useless.
In this case those lines would...end in nothing but just stress on Aerith's will to be a normal human girl? The usual and obnoxious "red herring" that often fans apply to Aerith's character arc, as if everything concerning her feelings and expectations for the future were just a literary device to make her death hit harder?
I think there's something more.
Let's be clear, even IF the Remake will take a different direction than the OG and leave Aerith live, I think there are no chances Meteor won't be summoned. If anything because it's...the symbol of the story itself, it may sound simplistic but it's a matter of fact.
On a deeper level I'd point out that the symbolic dualism between Aerith and Sephiroth - that later will lead to Holy vs Meteor - has already been abundantly shown in Remake part 1. Aerith and Sephiroth are the two key characters with knowledges about a post AC future, they both present features and motivations that stem from Case of Lifestream Black and White. I'd say this is also a good reason to believe Aerith's fate can't be changed because her role as Sephiroth's counterbalance is set in stone, and I think this is quite the point of this character, accepting to be the embodiment of the spirit of rebirth and preservation, the true Cetra against the fake Cetra, the son of Jenova, who symbolizes oblivion and destruction. The yin and the yang of the FFVII universe, while Cloud, a completely normal human being who happens to be both the "living legacy" of a hero related to Aerith and the perfect Sephiroth clone, is in an unsteady balance between these two forces.
But I'm getting off topic.
Contextualizing that line in the original flow of events, I think it can take a way deeper meaning and the answer is already before our very eyes.
Common human beings descend from the Cetras, yet lost all their powers. They can be considered as a bad evolution, a sort of involution due to the loss of the connection with Nature in favour of an easier materialistic life.
This lifestyle culminated with the creation of Midgar (deriving from the epic Midgard, the "realm of humankind") and the reactors that suck the lifeblood of the Planet itself in exchange of comfortable lives.
The Cetras managed to save the Planet from the Calamity from the Sky at the cost of their own lives, and now humanity is draining the Planet of its most precious element, reactors are turning the Lifestream in a tainted substance that causes the rapid growth of monsters. Even without Sephiroth and Jenova, the planet would die prematurely. Groups of dissenters joined into Avalanche to try to stop this process in an aggressive way that caused deaths and destruction as well, the salvation of the Planet often turned as a pretext to take revenge against Shinra.
Holy is the ultimate resort, whose role is not only to contrast Meteor but to cleanse the Planet of all threats. And this kind of parasiting humankind would be doomed for sure if it were not for this little group of people, each one on their own internal journey to discover and embrace the importance of preserving the Planet and the Lifestream. Aerith is the lead of this journey of rediscovery (and self-rediscovery) that she passes on all the others after her death.
No one but a delicate yet strong flower girl finally saves the Planet leading the Lifestream to support Holy and reject Meteor, and the Planet decides to give humanity a second chance.
The price is high though, during the following two years people struggle to start over. The survivors of Meteorfall are now decimated by Geostigma and Aerith alone can't stop Sephiroth's plans. Geostima affects especially children, those who didn't die because of the disease got under the control of the Remnants. The only kid who seems to be spared is Marlene, the one who more than anyone else carries on Aerith's legacy.
It has been rumored more than once that Marlene could be a Cetra. I'm starting to guess if the point could actually be that Marlene is instead a human girl who has learnt, through her special bond with Aerith, how to find that lost connection with the Planet that drew the line between humans and Cetras.
Sephiroth tried to rise again using kids, parasiting their minds to find the remains of Jenova; the same way Aerith announced Sephiroth's defeat through the kids, asking them to wait for Cloud to come back from the Lifestream. Hundreds of kids are framed enlightened by a warm light while they get to the church, Marlene and Denzel in the lead.
Not causally the name of the movie is Advent Children, and not causally Crisis Core and the Remake kept linking her to children.
I think that this is what that line is hinting. Not a biological kid to whom physically give the globe of White materia, but a new generation aware of what has to be done to deserve the survival allowed by the Planet, conscious of the importance to preserve the cycle of life. People willing to find the lost connection with nature and live in harmony with it.
Aerith's living legacy.
Just my two cents.