Became good friends with the Boy Who Lived

It's ridiculous that a time traveler becomes good friends with the boy who survived? It must be ridiculous! Cao Nan traveled to a world due to sudden death, and changed his name to Aris Grindelwald. Will Dumbledore die tragically? Impossible! Absolutely impossible! Will Snape die at the hands of Voldemort? Absolutely impossible! Will Sirius die? Will one of the Weasley twins die? Will the Lupins die too? JK Rowling is just a novelist, what does she know about the magic world? Cao Nan or Aris vowed to sharpen all the knives in this magic world, everyone~ let's enter this magical world together~...