The Horseman of the Absolute End

Insane Male Reader x Highschool DxD.
Y/N was ones a normal and happy person, who lived with his siblings. But one event changed it all. He and his siblings became the four Horsemen of the Apocalypse. Y/N became the Horsman of Death but he went insane, killed his three siblings and took their power. Striving for more power, he continued to kill devils, angels, fallen angels and even dragon gods to gain their power and Sacred Gears. What will happen if he meets a group of devils, who try to save him? Will he just kill them like the rest? Or will he become the normal, loving person who he once was?
Disclaimer: I don't own anything. Just this story.