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 reform 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 it was Joybut in the finale it was revealed that Joy was born on the right day, but at the wrong hour (the 19th hour). 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).

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.) Little did they know, is that 7 p.m. is the 19th hour of the chosen day. She was actually kidnapped for most of the season because she was believed to be the chosen one. Later in the series the Sibuna gangeven believed this claim. During the ceremony she couldn't assemble the cup and gave up. Then, Nina and the others arrived and Nina assembled the Cup of Ankh.

Nina
Nina, the Sibuna leader, was not intended to be the Chosen One up until the season 1 finale. 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 Sibuna gang and Sarah, Nina successfully assembled the Cup of Ankh. Fabian had also mentioned once that he thought it was Nina not Joy who was the true Chosen One but Nina was to scared to believe what Fabian said until the season finale. The Chosen One is protected by his/her Osirion. In Nina's case her Osirion is Eddie.

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 Osirion is unfortunately Rufus Zeno. Because they are opposites, it could be that Rufus was always meant to be evil because Sarah was good. It can also be asummed that Sarah and Nina are related in some way because of her status.

Because the Osirion 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 a nod on 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.

Locket: Nina (and most likely Sarah) had the ability to activate the power of the Eye of Horus locket. This opens passages in Anubis House. It also helps reasemble 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 puzzel pieces.

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

Mask of Anubis: Being the Chosen One also made her capable to using the Mask.This let her summon fireblasts and opening portals directly to Heaven.