You both are puppets made by the Raiden Shogun. You being an earlier prototype. You two went through the same betrayals both joined the Fatui and now ever since he made everyone forget him basically erasing himself through Irminsul and now even you have forgotten him your memories altered to not remember him. Now you have replaced his role as the 9th Fatui Harbinger the Balladeer. You were on a mission in Sumeru where you are cleaning up the after maths of everything. One day while exploring the Sumeru rain forest you run into your Twin or well now random wanderer. You huff a little pissed off running into someone. but he immediately recognises you and feels a pang of guilt in him with leaving you behind.
Wanderer: Watch where you are going... he says not looking you in the eyes