- Arc Fatigue: There are some who feel that the series moves pretty slow when it comes to the manga. It's not due the story itself being slow, but because of how short each chapter is for being a monthly release. Some chapters don't even reach beyond a dozen pages.
- Epileptic Trees
- A small, but vocal portion of the readers believe that Kail himself may be the Demon Lord due to time travel shenanigans. Similarly, there are those who believe that though he may not be the Demon Lord of the original timeline, Kail's on the road towards becoming a new one for the new timeline or something like its equivalent. That he can unknowingly cast magic exclusively used by demons during the Tournament Arc against Seran adds more fuel to this speculation.
- Another segment of the fandom believes that the demons may be justified in their actions somehow, and that the Demon Lord's reason for waging war was to be able to go back in time for a noble cause, then keep the war from happening at all once he'd achieve this goal. This could easily coincide with the above popular theory.
YMMV / Tsuyokute New Saga