Satan Satanel has been forced to rule the Red Kingdom on the peaceful planet of Ayuzuma for over two thousand years, and he's sick of it. He yearns for a day he can finally step down. After how long he's managed to rule, he feels he's earned retirement. Arsene Mendoza's two sisters have been missing, her eldest for over two thousand, and her younger for ten. She deeply misses them, and wishes for the day they could be reunited. Luck doesn't seem to be on her side. Nicolaus Astraia is technically the bodyguard to both Satan and Arsene, but nowadays, he's mainly Arsene's. After many years pining after Arsene, he ponders whether it's time to confess. And how to best lose weight. He can't stand to look at himself in the mirror anymore. Takahiro Koizumi used to be one of Satan's best friends, until Satan had enough of him. After spending almost a month in a depressive episode, he finally starts to feel a bit like himself again. After bearing witness to Takahiro's depressive episode and his almost-suicide, Katherina is out for revenge. Together, Takahiro and Katherina aspire to not only take over Ayuzuma, but the rest of the galaxy. Satan is forced to learn about the planet he saw as his prison, and teach the Ayuzumans how to fight in a war. After all, they haven't had a war in eons. Can fighting for Ayuzuma change his mind, or will he always be bitter towards Ayuzuma?