The Chosen One

The Chosen One is who was the only one who could assemble the cup.

Joy
All the way through the series, The Secret Society believed that Joy was the Chosen One. In the latter stages of the series the Sibuna gang believed it too. During the ceremony she couldn't assemble the cup and gave up.

Nina
Nina, the Sibuna leader, was not thought to be the chosen one up until the series finale. She was the chosen one because she was born on the true seventh hour, 7am not 7pm, in the seventh day of the seventh month. She successfully assembled the Cup of Ankh. Fabian mentioned once that he thought it was Nina not Joy who was the true chosen one.