Finally finished it! That final arc was unnecessarily long. Once the male lead became the Dimensional Rider, it was just non-stop twists that pushed the "plot" forward without explaining anything.
As far as I can tell, the mom hated her daughter because she reminded her of her ex-husband, so she tried to kill her. But due to the girl's power, dying kept resetting time, so she kept killing her in multiple ways, but the time resets everytime , which drove the mom even crazier.
Still, I have no idea what any of that has to do with the Dimensional Rider, an entity created by the girl's wish to die before Day 8 to reset time , to prevent the destined death of the portagoinst in that .
It's frustrating how such a simple concept got stretched out over 30 chapters of nonsense.