SVSSS AU where there is a system error when transmigrating Shen Yuan, so instead of being Shen Qingqiu, he's just a random NPC, but Shen Qingqiu still suffers from a qi deviation and does actually lose his memories. Shen Yuan, who looks like Shen Qingqiu due to the botched transmigration, decides to take advantage of the memory loss and goes to Cang Qiong and claims to be Shen Qingqiu's long lost brother. Yue Qingyuan is sceptical, but all the other Peak Lords believe him and allow him to stay with Shen Qingqiu. Shen Yuan eventually gets him to agree to allow Shen Yuan to look after his disciples and he starts by making Luo Binghe's life less miserable.
Shen Qingqiu does eventually regain his memories, but he never calls Shen Yuan on his bullshit, in fact, he plays along and acts like he's been looking for Shen Yuan for years. He even tells Yue Qingyuan that Shen Yuan is an actual brother and that he could fuck off with his accusations.
Shen Yuan believes that he was able to trick Shen Qingqiu, but in reality Shen Qingqiu is lonely and likes having Shen Yuan as company, plus he no longer needs to train the disciples which was a job that he hated
He still doesn't like Luo Binghe, especially now that he takes a lot of Shen Yuan's attention, but Shen Yuan likes the beast so he doesn't do anything about it
(years down the line the Abyss arc still had to happen, but when Luo Binghe returns it's not to kill Shen Qingqiu, but to fight him for custody of Shen Yuan)