The Just Because! (Jasuto Bikōsu!, ジャストビコース！?) manga is written and illustrated by Kamaboko RED. It ran for the entire tenure of the anime's airing. It was released with other short story chapters into an anthology on January 14, 2018. 
|Original Run||September 2017 – December 2017|
It is winter of their third year of high school, near the end of the second semester, when students have very little time in high school left. Everyone is just waiting for graduation. Until he suddenly came home. He was their classmate in middle school who had moved far away. He transferred in at a peculiar time, which reunited them. It was as if a go signal rang out to the feelings of the students who had just thought their high school life would end without fanfare.