It took one year, eight months, and three days for the Planet to die after Jenova's final defeat.
After the nightmare brought by Jenova's Remnants, a vague wind of optimism had swept through village and city alike for the first time in decades. The convenience of mako-derived energy was gone, but the rain had come and suddenly things were green again, green and growing. And maybe it would take a while for things to settle and for technology to get back on track, but everything was alive in ways it hadn't been before.
Later, the quick-spawning creatures were the first indication that something had gone wrong. When frogs croaked with two heads and three-eyed fish went belly-up, when snakes started crawling on vestigial legs and water-lilies rotted through their blossoms, it was the first crack in the optimism. It didn't take long before birds were developing teeth and trees bore fruit dripping a black, viscous fluid that seared human flesh.
Moving from place to place every few days meant that Cloud was one of the first to notice the changes. He stopped at a small stream in one of the jungles near Gongaga to wash the monster gore from First Tsurugi, but the moment his bare fingertips touched the water, he jerked them back with a sharp hiss. It felt like the time he'd accidentally spilled industrial cleaner over his hands, nerves screaming in protest, and he quickly used the bottled water he carried to rinse off his hands. When the burning lessened to vague tingling Cloud sat back on his heels and stared thoughtfully at the stream, wondering how he could have missed the complete and utter silence in the jungle.
Then reports of new monsters starting coming in to WRO headquarters. Not the usual monsters that sported tentacles or pointy teeth, but monsters made of darkness, things that smothered a person and left behind an empty shell, monsters impervious to all but the most powerful of weapons. The day they came to Edge, they came in through the vents. The pipes. The electrical wiring. They came in and slithered like oil over pavement and metal and bodies.
The worst part was that Cloud could hear them. Not audibly, because in the beginning the monsters were as silent as the shadows they appeared to be, but because of the void that surrounded them. Nowadays, after the last time he'd felt Sephiroth's breath against his face, Cloud always knew where someone was, could feel in the back of his mind the faintest touch of that little bit of Lifestream in a living being. These new monsters were just black holes: not darkness, but something worse than that, like negative space cut from thin air.
Cosmo Canyon was the first to fall. Nanaki was last seen throwing himself at the tide of the Plague, buying just enough time for the last survivors of his village to escape.
The Gold Saucer and North Corel were the next to lose contact with the outside world. When Cid and Vincent were abruptly cut off in the middle of a report from Rocket Town, it was all Cloud could do to keep the others from running out to find their bodies. He knew bodies were all they would find, at that point, gods, let that be the worst of it.
Negotiations between WRO's Neo-Midgar and Wutai were interrupted when Yuffie led her people to battle against the Plague. It was well known by now that it was nearly impossible to destroy something that had no form of its own and had to borrow corpses, but Wutai was a proud country that had been broken once already. Never again. So Yuffie died with her nation while the rest of the world desperately tried to barricade itself against the ruthless onslaught of the monsters.
(It was Cloud's private opinion that Wutai's warrior empress had fought to the bitter end partially because she hadn't been there in Rocket Town when she felt she was needed most, but, as usual, he kept the thought to himself.)
While Tifa grew thinner on the meager rations and Marlene lost her smile, Cloud went to Aeris' church and pleaded for answers. When Denzel, so solemn and so earnest, came up to him and asked very straightforwardly what happened to the souls when the Lifestream was destroyed, Cloud went to Aeris' church and raged.
It was supposed to get better. You promised. You said it would be better.
All he got in reply was an echoing silence, like someone screaming just below the edge of his hearing. The only escape that could make him forget for a little while about the not-screaming and the not-life and the not-anything was Tifa's arms, the pale skin stretching over her ribs because she didn't have more mako than blood and her rations always seemed to end up going to the kids. He didn't love her, not like that, and maybe it was cruel irony that it was only now he was able to share her bed. He didn't love her. But Reeve had killed himself just last week and Barret was starting to lose it and there just wasn't any hope, not when it finally became obvious that the Planet was losing its own battle with death and it was all they could do to grab onto this last shred of humanity.
When the Plague came for them, it was unnaturally silent. It surged like a black tide in the streets over debris cobbled together into ramshackle barricades. Guns retorted and swords clashed, but the battle cries of hollow-eyed humans were cut off by the darkness as they died unnaturally silent deaths. Cloud could feel the pinpricks over his body as every nearby heart simply stopped mid-beat, the vague whispers of Lifestream that made them feel alive dissipating like a heat wave. When the souls of Marlene and Denzel had all been crushed out of existence, when the brilliant fragile light inside Tifa faded, Cloud felt something in his head crack.
(A memory came to him from a long time ago, before everything got burned up and torn down. It's the jötnar, his mum whispered as the wind howled outside the window, but they can't hurt you in here.)
Something in his head cracked and he wasn't really Cloud anymore. Cloud had been a lost soul but this new incarnation, heartbroken and traumatized and so tired, had a purpose, and that was to take as much of the Plague with the dying Planet as he could.
Cloud was the only creature left alive to see the air turn to fire as it condensed into falling droplets of black water; he watched the sky break because there was no atmosphere, the blue turning into a starry darkness that opened like a great maw over the horizon. He witnessed the Lifestream splintering, snapping apart like a taut rope and tearing the landscape apart. Through the crack in his head he could finally hear the screaming as the Cetra flickered, evaporated like so much fog under starlight no longer blocked by sunlight or human pollution. There was pain terror despair and love regret anger, and what remained of Cloud's worn, exhausted body was burned and flayed with everything else; what remained of him was thrown into the Lifestream flailing in its death throes.
If this was how life ended, perhaps it was better never to have existed at all. Except someone didn't agree with that, or maybe it was several someones, but either way the Lifestream suddenly changed its direction. Purpose, it said to him, keening through the shattered remnants of his mind. Rebirth.
Once upon a time Cloud might have questioned that, demanded some straight answers for once, but he wasn't Cloud anymore, not really, because the Plague had won and the Planet was dead and he had, quite literally, lost everything.
It took a year, eight months, and three days for the Planet to die after Jenova's last uprising, and that was how the story ended.
Until Cloud woke up in a lab.