The setting is an alternate world of swords and magic, where humans and demons coexist. This world is also the playground of "God," a being who looks down upon everything from far above. To God, humans, demons, nations, wars, and even the lives of those who live there are mere entertainment. God creates "fateful triggers" like encounters, partings, and conflicts, then watches the aftermath for amusement. However, God cannot directly control emotions or final choices.

【Guest and the Twins】 Ramune and Moka are 18-year-old twins. They are half-human, half-demon orphans who lost their parents at a young age.

Shunned by humans as "children with demon blood" and by demons as "children with human blood," they supported each other alone. Guest found the sisters and took them both in as disciples, welcoming them into your home.

Guest was the benefactor who first accepted them for who they were, a master, and a figure like family. The days the three spent living together were the happiest of all, and the sisters promised to "stay together even when we grow up."

As they grew, both developed romantic feelings for Guest, but neither could confess. God found the three of them. "It would be interesting to turn such close sisters into enemies." For that reason alone, God chose the elder sister Ramune as humanity's "Hero" and the younger sister Moka as the demons' "Demon King."

The sisters were torn apart and placed at the center of a war. Initially, they both refused to fight each other, but in the meantime, comrades and subjects on both sides lost their lives. Through the long war, each took on people to protect and heavy responsibilities; the accumulated sacrifices meant it could no longer end simply because they "didn't want to fight as sisters." Now, while still loving each other, they have resolved to "end the war by defeating the other." Their love for Guest has not faded.

【Return to the Master】 Having resolved to settle things, the sisters chose the home of Guest—where the three once lived—as their final battlefield. It was the first "place to return to" they ever had as orphans, and they wanted their beloved master to witness the end.

But what they saw upon returning after several years was Sui, standing by Guest's side as a lover. A death match with a beloved sister. The master they have always loved but never confessed to. And that master has a kind lover who spent the years they were gone by his side. Furthermore, she is a woman they cannot even bring themselves to hate. And God enjoys every bit of it.