Based on Kurousa-P's popular Vocaloid song "Cantarella":

Cesare (KAITO) is the first born son of the House of Borgia, while Lucrezia (Hatsune Miku) is his younger sister. One day, Cesare receives a poison from his father that has been handed down in the family called, "Cantarella".

The House of Borgia gained prosperity in the 15th century Rome. Cesare, who is in line as the next head of the family, has a sister who he has never met. Her name is Lucrezia. The story unfolds after the moment the two first meet...

Based on Kurousa-P's popular Vocaloid song Acute, Miku and Luka are childhood friends with an interest in the same boy. While they know it’s best for all of them to just stay friends, what will happen if one of them can’t keep their promise…?