The Chosen One

The Chosen One is the only one who could assemble The Cup Of Ankh.

When the cup was broken into seven pieces, Anubis made an agreement with Amneris that once every 25 years, on a special date, at a special time, a member of Amneris' bloodline would be able to reconstruct the Cup of Ankh. This person would be born during a certain month, on a certain day, and a certain time, which all fall on the same number (example: Sarah Frobisher-Smythe who was born during the first month on the first day during the first hour). It was originally believed that the Chosen One was Joybut in the finale it was revealed that Joy was born on the right day, but at the wrong hour (the 19th hour - which is also known as 7pm.).

The true Chosen One is Nina. It is shown that the Chosen One might have powers relating to seeing ghosts and spirits. The Chosen One also has an opposite who is called the Osirian (Eddie, for Nina). The Chosen One is also probably very loyal and of pure heart as both Sarah and Nina would do anything for their friends and Nina could enter the Egyptian afterlife while Rufus could not. The Chosen One and Osirian can't be together because 'bad things can happen'.

Joy
All the way through the first season, The Secret Society believed that Joy was the Chosen One because she was born on July 7th, at 7:00 p.m ''(which they thought was the seventh hour but is truly the 19th hour). '' She was actually kidnapped for most of the season because they were scared that The Betrayer (Rufus) would find her. Later in the series Sibuna believed this claim as the truth. During the ceremony Joy couldn't assemble the cup and gave up. So did the Secret Society. Nina, being born on July 7th at 7 a.m. made her the Chosen One. Then Nina and the others arrived and Nina assembled the Cup of Ankh.

Nina
Nina, was not known to be the Chosen One until the end of Season 1. She was the Chosen One because she was born on the true seventh hour, 7am, not 7pm, on the seventh day of the seventh month. With the help of the Sibunas and Sarah, Nina successfully assembled the Cup of Ankh. The Chosen One is protected by his/her Osirian, who also hears voices like the Chosen One. In Nina's case, her Osirian is Eddie.

Sarah Frobisher-Smythe|Sarah
In House of Strategy / House of Memory it is revealed she was once "The Chosen One" She was born on January 1st at 1:00 in the morning. She gave Nina a special locket to find "treasure" in Anubis House. Sarah's Osirian was Rufus Zeno. Sarah and Nina are related in some way because they are the Chosen One and the Chosen One is someone from the Amneris' bloodline. Because the Osirian refers to Osiris, it can be assumed the Chosen One could be a nod towards Isis, goddess of magic but this is unlikely because The Chosen One is actually in the bloodline of Amneris, the high priestess. So it is assumed the Chosen One has another protector, someone that represents Isis.

Powers
Mediumship: Nina has the power to talk to ghosts and see them, such as Sarah, Senkhara and Victor's father. She can also see spirits like Senkhara.

Locket: Nina (Sarah for part of season 1, and Eddie in season 3) had the ability to activate the power of the Eye of Horus locket. This opens passages in Anubis House, as well as opens certain clues. It also helps reassemble the Cup of Ankh.

Cup of Ankh Assembly: Being the Chosen One, she is the only one capable of recreating the Cup from the broken puzzle pieces.

Accidental Release of Spirits bound to the Cup: When Nina attempted to stop the Cup from glowing, she accidentally released Senkhara.

Visions: Like Eddie, Nina is able to see things that interpret the future and have hidden meaning.

Mask of Anubis: Nina is capable to use the Mask of Anubis to enter the Afterlife, as well as use the mask to create Tears of Gold.

Voices: Like Eddie, Nina could hear voices in her head giving her advice when she needed it.

Talking to the House: Nina could connect with the House, and receive messages from it.

Trivia

 * In all versions, all Chosen Ones have been primarily of the female gender. No male Chosen Ones have been featured yet, though Osirians are similar to Chosen Ones.
 * The Osirian is the Chosen One's protector.
 * Sarah's Osirian was Rufus Zeno, and Nina's Osirian is Eddie.