The conflict between Cloud and Sephiroth in Final Fantasy VII and Final Fantasy VII Remake is rooted in events that happened thousands of years before the start of the game, dating back to a conflict between the Cetra and Jenova. All that remains of the two foes in the present day are Aerith and the frozen body parts of Jenova.

The reason Final Fantasy 7's Shinra Electric Power Company wants Aerith so bad is that she is the last-known member of the Cetra species. The Cetra were the magic-using dominant species on the planet. Cloud and his friends witnessed a manifestation of the Cetra in the Temple of the Ancients and it resembled the classic Black Mage design from the first entry in the series. If Ifalna (Aerith's biological mother) is a full-blooded Cetra, then the species resembled regular humans. The Cetra depicted in the hologram video seen FF7 Remake also shows them as resembling humans, though it's unclear how accurate this footage is.

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The Cetra would have remained the dominant force in the world of Final Fantasy 7 were it not for the arrival of interstellar threat. Three thousand years before the events of FF7a creature called Jenova crash-landed onto the planet, creating the Northern Crater in the process. The Cetra investigated Jenova, which led to their downfall.

FF7: The War Between The Cetra & Jenova

Final Fantasy VII Remake Cetra Hologram

Jenova is an alien monster with the ability to control other lifeforms by infecting them with a virus that controls their DNA. Jenova also possessed a high level of telepathy and shapeshifting abilities. According to legend, Jenova used this ability to get close to the Cetra and spread her virus throughout the species, transforming them into monsters in the process. A small group of the surviving Cetra managed to defeat Jenova and seal her away in the Northern Crater, but much damage had already been done and the Cetra were nearly wiped out. A popular fan theory states that the group of Cetra that defeated Jenova went on to become the Knights of the Round summon, but that has since been debunked by the creators of the game.

The number of Cetra dwindled over time, as the native humans became the dominant species on the planet. As of FF7 Remake, Aerith is the last remaining person with Cetra blood, even though her father was a human. Jenova still lingers on in the world, as her DNA was used to give the members of SOLDIER their special powers. Sephiroth was injected with Jenova's cells while still a fetus, giving him access to many of her abilities. This means that the struggle between the Cetra and Jenova is continuing into Final Fantasy 7 Remake's modern-day, through Aerith and Sephiroth.

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