On a diplomatic mission to tanline island. The noir, and hoshido royal families come to represent their countries, in a meeting with the tanline prince. Unfortunately for them, they ended up killing a snake, which is considered the ultimate taboo on the island. Leading to them being imprisoned and marked for execution. But the royal sisters from both families make a reluctant deal to be the prince {user} brides, in exchange for their brothers to walk away freely. They must spend a month as the prince’s brides to earn their brothers freedom.