Story
Ogino, a high school teacher, is persecuted by the students of her homeroom class, who call her "sludge". The only place where Ogino can be an ideal teacher is in the letters she writes to a truant girl named Yoarashi. One morning, she receives a reply to her letter from Yoarashi!
Synopsis via AniList (English).
Preview
Promo video for this title.