Not only a dream about her death, but just as much about his failure to prevent it. A persistent traumatic memory, the recurring dream preserving the original trauma with remarkable clarity, even after centuries. Survivor's guilt, the kind of which no sedative in Teyvat would combat.
His lips pursed in disapproval. He didn't wish to talk about his past. It wasn't that he had forgotten about Katya. It was that he was afraid of how he would feel, once he began discussing that subject. Her death was his biggest regret. The thing that haunted him, even centuries after it had +