Parabellum

On the very first day that Kuze Aoi transferred to Hinomiya Academy, he finds himself facing down the barrel of a gun. He is introduced to the campus and the student body by his childhood friend Miyabi and learns about the prince and princess among students, Shitara Sagiri and Hinomiya Kuon. Sagiri is a cool and beautiful while Kuon is elegant and magnificent. After school, Aoi gets lost on campus and Kuon begins shooting at him and he's barely saved by a random girl named Atarashi Sonoko. It seems that Aoi holds a secret that is critical in a feud between two old, powerful families.

(Source: MangaHelpers)