Talentless Nana

Plot

An academy on an island in unnavigable waters. There, students trained tirelessly, to fight back against the enemies of humanity. The protagonist, a student newly transferred there, also sets out with the intention of eradicating all enemies of humankind. An unpredictable, intellectual suspense story of justice and evil.

https://www.crunchyroll.com/comics/manga/talentless-nana/volumes