Phoenix was dragged back to Equestria, along with three friends, for a reunion with Twilight. However, the next day shattered the sunny theme when a little filly from Canterlot raced to Ponyville to asked Phoenix for help to defend her older sister, who was accused for a crime. Phoenix, however, did not expect the 'older sister' is actually a familiar friend...

This takes place a year after BoBoiBoy The Movie II. BoBoiBoy finds out that he is not the only one wielding all seven Elements. And yet, he will uncover a new hidden mystery. It's a mystery he won't soon forget, as it will bring him to someone new, who happens to have a key connection to a certain villain he thought he would never see again. "... Who Are You?"