It was probably that Sarana found Itachi's diary one day when she was looking through Sasuke's old belongings.
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I have also posted QAQ on hinmoe.
Last time, I revised the copy but I don't know why it didn't change...
It's over in just one chapter.
Generally speaking, the routine is quite similar to "The Diary of Izuna" written by a certain author.
Conception: