Ogasawara Hiroki was a thoroughly ordinary man, until one fateful night, where - quite inadvertently - he learns of the existence of succubi.
After meeting and wooing a series of succubi, Hiroki is now prepared to settle down with his harem and enjoy a quiet life. Fate, however, has other plans, after Hifumi becomes embroiled with Princess Stephania Sofia Maria Isabella: a noblewoman who hails from the small European country, Astoria.
Stephania, as it transpires, is a big fan of Japan, and of Japanese culture, and - having lived an isolated life within the palace's walls - she's overjoyed at meeting a Japanese beauty like Hifumi.
After tasting defeat by Hifumi's hands in the karuta championships, Stephania extends an invitation to Hifumi. Stephania asks Hifumi to stay with her in Astoria, so she might teach her about karuta, and share with her stories about Japan.
Not wanting to travel to Astoria on her own, Hifumi invites Hiroki alongside her, and - through a series of happenstances - Marina and Hazel find themselves tagging along for the ride.
In Astoria, Hiroki meets and befriends both Princess Stephania and her dutiful maid, Elizabeth. The days pass, and both the princess and her maid begin to show an interest in Hiroki. There's something a touch unsettling about Elizabeth, however; something which immediately catches Marina's attention.
Could Elizabeth be more than she's letting on - and what, exactly, is she scheming?