Advent ChildrenThe continuation of the Final Fantasy saga comes to us in the form of Advent Children. Seph reappears in FF7, after Kadaj is doused with the cells of Jenova, showing that Sephiroth's will is amazingly powerful that he can escape death itself. Sephiroth, not content with becoming a puppet to Jenova, had long since FF7 taken completely control over Jenova's cells. Kadaj became Sephy, rather than Jenova because Sephiroth proved to have a stronger will, possibly inherited from his biological mother Lucrecia. Sephiroth has overtaken the will of Jenova, giving him complete control over Jenova's cells and power.
Despite being dreadfully outmatched, Cloud defeats Sephiroth with the power of the dead Aeris watching over him. By this time, though, Sephiroth has become so unified with the planet and with Jenova that he can never be defeated until every last memory of him is gone. He vanishes, but will likely appear again, as he is very intricately infused with the power of the planet and with Jenova's cells already.
Sephiroth's appearance in Advent Children is very iconic, and he displays an amazing amount of raw power, toying with Cloud throughout much of their battle.
Final Fantasy VII
Final Fantasy University
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