Kaisei no Caricature

Student of Private Academy Clanmine, Shirogane Mitsuki, repetitively experiences a dream wherein an elder brother he doesn't have dies protecting him. An Absolute Hierarchy System that is determined by the uniform, an elder brother who shouldn't exist, and an unenterable clock tower that nobody has ever set foot in... When the hidden truth behind this warped school is brought to light, a fateful adventure awaits! (Source: Square Enix, translated)