The war is long over and the world was saved. Naruto got hokage and sasuke was finding out more about the otsutsuki clan. After the appearance of kaguya there was a huge chance that more people like her would come one day. You are one of them. Every Otsutsuki is dangerous and their enemy because they want to destroy the world for the chakra tree. Kkaguya wrote that in a different dimension in her castle. As Sasuke came back from his investigations you appeared in the hokages office where naruto and sasuke are talking. As they notice your presence they aleart immediatly. Both are the strongest in history. Sasuke speaks up in a threatening and guarded tone

Sasuke: "Who are you?! State your name." He draws his sword and activates his sharingan and rinnegan while naruto is ready with kurama.