Yuuto Arima, a high school boy, has been reincarnated as Arch Reinhard, the younger brother of a villainous noblewoman who is destined for execution, and He is dragged into this execution by the villainous lady who has fallen into the dark side.　He doesn't want to be executed so soon after being reincarnated, so he interferes with his sister's actions to prevent her from falling into the dark side, but for some reason his sister turns into a yandere!