This article is for Jack Twombly as he originally appears. For the Jack Twombly that appears in Chapter 5, see Irving Onegin.
Jack Twombly, known as Sakutarō Ninomiya (朔太郎 二宮) in the Japanese version, is a teacher at Kako High. He is introduced as Ethan Kairos' homeroom teacher, and he appears frequently in-game, giving Ethan advice along the way. It is later revealed that Jack was also Derek, Irving and Timothy Kairos' homeroom teacher in the past.