Chapter one:
Alexandria Kline (born May 18 2017) is the daughter of Michael and Kaida Kline (who was possessed by a demon, in order to kill Michael.) She is the first only known Nephalem to be sired by an Archangel and a demon. Her cousin, Jack is the first only known Nephilim to be sired by an Archangel. Both Jack and Alexandria was taken in by Sam Winchester and Dean Winchester who would teach the cousins how to master their powers. During this time, Jack and Alexandria both played a role in the resurrection of Castiel who they had chosen to be their father.
Due to her birth, it lead to the creation of the Oni demons, something that both angels and demons stated that it is impossible for someone like Alexandria to create a monster like that.
Alexandria would stay with the Winchester's and Castiel as she master's her new powers, in an effort to prove she is good and not like her father, Michael and try to help track down Jack. During this time she had formed a brother\sister bond with Sam, developed her daughter and father bond with Castiel. She later formed a romantic bond with Dean Winchester.
According to Castiel, Alexandria is one of the strongest kind of half breed's and she is capable of overpowering almost every kind of creature sent against her.
Alexandria is also the granddaughter of God and according to the angels- Lucifer's favorite niece. She's also the surrogate daughter of the Angel Castiel and a member of the Winchester family.