Cantarella

Cesare, the eldest child of the notorious Borgia household in fifteenth-century Italy, learns he has a sister he’s never met—Lucrezia. He is also given a poison called “Cantarella,” which has been handed down in the family for generations. The story unfolds after Cesare (here played by Kaito) meets Lucrezia (Hatsune Miku) for the first time… (Source: Seven Seas Entertainment)

Based on Kurousa-P's popular Vocaloid song "Cantarella" and its subsequent musical adaptation.