Kuwazuru Mitsuki is a second year student at Arakawa Nishi High School. One day, her homeroom teacher, Tachibana, suddenly announces the start of the "Letter Game", where every student has to write a letter with his/her true feelings to each of the classmates. However, the "letter" will not include the sender's name. At first, there were a lot of bad jokes and silly "letters", but they slowly accelerate to revealing secrets and confessions, which make everyone question, "Who is the sender?" and "Who will be named next?" This game allows the students to become more aware of each other's hidden worries and thoughts, which slowly deepens the bond among the classmates. Meanwhile, Mitsuki tries to search for the sender of the letter sent to her and she discovers a secret hidden in this "letter game".
Sanari, born in Tokushima Prefecture, is a Japanese rapper and vocalist who started making YouTube videos in his early years of elementary school. At around the same time, he encountered rap and started freestyle rapping with his friends. When he entered junior high school, he started to make original music and posting original videos again. His debut album, SICKSTEEN was released on June 5th, 2019.