BBY/ABY is used to position items along the Star Wars Timeline. BBY refers to Before the Battle of Yavin. ABY refers to After the Battle of Yavin. The Battle of Yavin in Episode IV: A New Hope occured in 0 BBY/ABY.
Soon, BEN SOLO'S path will end in a place of fire and blood, and a shadow will rise to take his place. He is with the KNIGHTS OF REN now, and they will welcome him, if he can pay their price.
But before that destiny is fulfilled, a battle must be fought at an ancient JEDI Outpost on the planet ELPHRODA - between Ben and those who know what he could have been... and fear what he might become.
Fear leads to anger. Anger leads to hate. Hate leads to suffering. Everyone here is afraid - Ben Solo most of all!