I get that these flashbacks are probably necessary to actually understand the story... But they really kill the pacing when these show up mid-fight. Do we really need the full backstory for the body of the MC? It hadn't been important for 100+ chapters, and it really doesn't seem important to spend multiple chapters just to show the MC's body and show that there was a sword named Rafaello. "Ooh, wow, it's that name that the MC said a few times." Get on with it!
In possession isekai where the MC takes over the body of someone that just died, frequently the body is barely given a few panels of backstory within the first few chapters, and that's it. Not multiple entire chapters in a row...