Knights of the Zodiac

Sienna transforms into Athena because her cosmic powers activate uncontrollably when she experiences extreme emotional distress during the battle between Seiya and Nero. Her divine rage and the overwhelming threat to her life cause her to manifest as Athena, a goddess form that carries immense destructive power capable of annihilating the world.

Seiya stops Sienna by appealing directly to her humanity and love. He tells her that she can choose her own destiny and does not have to be controlled by her destructive powers. His words reach her compassionate nature, allowing her to regain control and revert to her human form, preventing the world's destruction.

At the end, Guraad is not killed but rather healed when Sienna shares her cosmic powers with her. Rather than allowing Guraad to die from her injuries or be destroyed, Sienna chooses to give her powers to Guraad, showing her the potential for salvation rather than annihilation. This marks a redemption of sorts for the former antagonist.

Nero betrays Guraad because he wants to kill Sienna and take her cosmic powers for himself rather than let Guraad use them. While Guraad intended to extract Sienna's powers to stay alive, Nero opposes this plan and decides to claim the powers directly, viewing Sienna as a threat to the world that only he should eliminate.

Yes, Sienna is alive at the end. After reverting from her Athena form, she survives and embraces her role as both protector and goddess. She makes the conscious choice to use her powers for good, preparing to face larger threats ahead alongside the remaining Knights of the Zodiac.

Yes, Seiya successfully rescues Sienna, though the rescue is complicated by the betrayal of Nero and Sienna's transformation into Athena. Seiya defeats Cassios and battles through Guraad's henchmen, ultimately reaching Sienna and talking her down from her destructive path, ensuring her safety.

Nero is left wounded but alive at the end of the movie. After his battle with Seiya, he survives despite his injuries. The ending explicitly indicates that this leaves the door open for future challenges, as Nero remains a potential threat or antagonist for future films in the franchise.

Sienna heals Guraad because she chooses to show compassion and the potential for salvation rather than seeking revenge or annihilation. After regaining control of her powers, Sienna decides to share her cosmic energy to heal Guraad's injuries, demonstrating her belief in redemption over destruction.

The ending clearly sets up a sequel by having Sienna realize she must gather the remaining Knights of the Zodiac to prepare for the return of the old gods. This establishes that their fight will continue in future films, with the main characters embarking on a new quest to face larger threats.

At the end, Sienna embraces her role as both a protector and the goddess Athena. She accepts her cosmic powers and chooses to use them for good, preparing to lead the Knights of the Zodiac against the returning old gods. She represents hope and a new beginning for the world.