Toumayhem by Crescendo

Toumayhem is a sci-fi/mystery visual novel set in Shigo Private High School, in Hokkaido; Yuki, a timid first-year, gets roped into a fight to overthrow the school’s social system, and mixed up in a series of murders.
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This game contains themes such as: murder, suicide, bullying, and heavy language. Also maths. I know some of you are turned off by that. Understandable.

Yuki Kourei enrolls into Shigo Private High School, between the mountains of Hokkaido, to start life anew far from his hyper-protective mother.
His plan goes awry when he discovers the school’s rigid hierarchy, in which the younger students must follow all of their upperclassmen’s orders; too nervous to join them, he’s completely cut off from the others and branded as Ghost.
Akito Ikeda, a fellow Ghost, persuades him to join the Spectral Brigade: a group of first-years who want to overthrow the current system. But nightmares and visions of someone dying haunt Yuki, and when a snowstorm cuts him and his schoolmates off from the outside world, these visions come true.
Yuki will have to win the trust of his schoolmates, discover who’s trying to kill them, and why…