Koiiro Soramoyou

The protagonist, Itou Seigo, son of famous scientists, due to his parents' circumstances and the construction of Kamina Bridge, moved from Tokyo to Kamina Island and transferred to Kamina Academy. He reunited with his childhood friend and stepsister. Moreover, in peculiar circumstances, he also met a cold beauty, wielding a Japanese sword; a member of the Disciple Committee with blond hair, who has an aura of seduciness around her; and the daughter of a rich family, who is also the head of the student council. And so his rich school life truly began, filled with hassles from the Disciple Committee, dreadful guards of school discipline, led by the severe and ruthless teacher Serizawa.

...But good things never last long. Following the arrival of the mysterious person on the island, cruel events began to occur one by one. At the beginning, Seigo was rather indifferent, since he had not much attachment to his new environment, yet the distress developed and involved the whole island. Not even his friends were left untouched...

Seigo felt fury against unreasonable adults and made a decision to fight for the academy and the whole island, which were precious to his dear friends.

[Translated and edited from pixiv]