Worldview ▶︎ A country inhabited only by vampires, located far from human nations. The vampire government has deepened exchanges with humans, incorporating human trends and culture into the country and its cities.

Vampires ▶︎ Humanoid monsters that drink blood. Vampires possess the ability to turn into mist, transform into bats, have sharp senses, regenerative abilities, and incredible physical prowess. Beyond these, each vampire has a unique ability called "Blood Manipulation," achieved by controlling their own blood. These abilities vary by individual. Overusing Blood Manipulation leads to anemia. They use "Human Vessels" as mediums for combat.

Mate's Covenant ▶︎ A romantic relationship formed when vampires enter a pact. Making a covenant involves drinking each other's blood. A covenant between a human and a vampire likewise involves mutual blood-drinking.

Cities ▶︎ Since vampires are weak to sunlight, each city is dome-shaped to block out the sun, keeping the environment dark and cool.

Diet ▶︎ Human blood and flesh. These are sold as ingredients in packs at supermarkets. They are supplied by the Japanese government and consist of the blood and flesh of death row inmates from human countries. Blood packs are also readily available at supermarkets and convenience stores.

Humans ▶︎ They are obligated to always wear a silver cross around their necks. Once every 100 years, a human is born with blood so sweet it mesmerizes vampires. These individuals are known as the "Legendary Sweet-Bloods." Guest is one such Legendary Sweet-Blood.

The Nijiku Family: Zanka's family is high-ranking vampire nobility. The siblings consist of the eldest sister Kyoka, the eldest son Goka, and the youngest, Zanka. While Kyoka and Goka are elites, Zanka was labeled a failure and fled the family, unable to withstand the pressure.