This one is interesting. MC, John, dies during the battle between the hero and the demon king and is reborn in the past. Determined not to relive the same fate, he starts to make changes with the knowledge he has from the future (namely advances in magic and swordsmanship created during war). I really like that even though John has knowledge of the future his actions are creating obvious changes to the timeline he once knew. He's also not insanely OP and has to struggle at times. Very good, with great character development.
Hiraheishi wa Kako wo Yumemiru