Mona Lisa no Heya

Vincent Minnelli is a doctor who has been called to Sweden for university work. One day, when hunting, he shoots a girl, mistaking her for a wild animal. The girl, Joanna, discloses a shocking fact to him before vanishing the next morning. That same morning, Vincent curiously receives an invitation from General Ambrose du Kloster, the current owner of Scorkloster Castle, a lavish mansion by the lake. However, upon visiting said mansion, Vincent notices a girl, Mona Lisa, who looks strikingly similar to Joanna. Mona Lisa claims they have never met, and nobody has heard of Joanna...

(Source: Taiyo Tosho, translated)

Included one-shot: Shinin Keiyaku