He didn’t want to go back too far in time either, since if he did, people’s memories of what had happened before the reset would disappear and they would just repeat themselves.

...

Curious about what they were up to, Mitsuki turned his attention to the twin goddesses and immediately noticed that something was wrong. One of the twins, Rilna, was nowhere to be found. Looking back to the reset, he saw that Rilna had never existed in this world. Assuming something was wrong, he checked the current number of people against how many had existed before the reset and found that a huge number of them were missing. Using his data processing magic, he analyzed those who had disappeared and quickly found his answer. Every one of the missing people had been killed by a boy named Yogiri Takatou before the reset.

Yogiri Takatou was a Sage candidate summoned to this world by Sion, and he possessed the ability to kill anyone just by thinking. Anyone killed by that power wasn’t affected by Mitsuki’s reset magic, so the world had rewritten itself to fill in the gaps.

With things going so far off track, Mitsuki couldn’t just stand back and watch anymore. He considered reviving the dead himself, but that would create contradictions in the new world’s history. In the end, the easiest solution would be to reset again, so he simulated a reset to see what would happen. The results were the same. No one Yogiri had killed came back.

-Volume 13 pages 43 and 44