Long story short, the main character had about 200 years to prepare for Aizen, and he ends up being too passive and just let things play out almost exactly the same like the anime did, with some very minor changes. This was honestly incredibly disappointing and made me drop the fanfic right there. I understand that maybe killing Aizen too fast might not let you continue writing an interesting story. But at the same time, it doesn't make a whole lot of sense for the MC to be this passive, especially considering his current power level at the time. The reason why we read fanfiction in my opinion is because we want to see some new interesting takes on the story, instead of just the same thing over again with some slight changes. After skimming through some of the later machine translations of future chapters, my opinion is that it doesn't really change significantly enough for me to bother, so I'll be dropping this here.