It had to have been fate. While on patrol for any ne'er-do-wells, Iroha runs into a demonic succubus named Lily, who forges a Pact with her: win the demonic proxy war as an agent for the succubi, and in exchange, any wish of Iroha's will be granted. Though Iroha's traditional duty is hunting down people disturbing public morals, she is now part succubus. Using her newfound demonic abilities, she has to grow stronger in order to defeat other humans who have made Pacts with demons - the Chosen. Will she survive, or will she suffer a tragic defeat at the hands of the other Chosen?