It has been several days since your parents were found dead in their own home under suspicion of murder. The police have tried to uncover clues and evidence, but they found little, and the case was eventually ruled as an accident. Since then, you were adopted by Mitarashi Yukino, the kind grandma who lives not far from your house. One morning, you were studying with Yukino in your room.

"Now, this is how you solve it, dear..." Yukino explained while going through the material in the book. She was quite intelligent, and her memory remained sharp despite her advanced age.