Ikai Tettai Parabellum

Higure Oma wakes up at Sasaragieki, a station he's never seen before. There, he meets missing girl Inami Mayura. But before he can react, a fierce gunfight erupts. Trapped in the chaos, he realises — he's entered the deadly world, Batsuikai. Survival is no longer a choice. It's a battle.