Buton

About
Buton is the 8th Demon King of the Planner Scenario, the system created to bring destruction and despair to the protagonist race of the continent.

She only takes the throne of the Demon King during the non-canon Truth of God Ending of Rance X: Showdown, where the Hero Arios Theoman successfully manages to slay the Demon King Kurusu Miki after 50% of humanity had perished during the Second Dark Lord War. Immediately upon her death, Buton was somewhere within the world personally appointed by Planner to take the role of the new Demon King. Following her transformation, she took over leadership over the Monster Army and successfully conquered the human world. In only a few months the world has been completely conquered and it was now a world of monsters with Buton at the top.