Satake Hirofumi is a prisoner on death row for murdering his fiancée. He's also an Undeadman who has survived many desperate situations. For this, he has earned the interest of a research institution called Human Crazy University, which studies real-life miraculous phenomena and the people who become entangled in them. Now a subject of their research, Satake relates to them his memories of his immortal, yet unhappy, life. Why did he kill his fiancée? Soon enough, the truth sheds light on a much bigger conspiracy... (Source: Crunchyroll)

When an extraterrestrial organism known as Savage attacks mankind, the only technology capable of combating the enemy is a weapon known as “Hundred.” A survivor of a Savage attack, Hayato Kisaragi is a teenager boasting the highest compatibility level with the aforementioned technology and as a result, is invited to master his skills at Little Garden, a prestigious military academy aboard a battleship. Over the course of his intense training for the battle ahead, he immediately attracts the interest of multiple female peers and gets drawn into a number of incidents as he tries to fight against the creatures that now inhabit Earth and threaten its safety.

Based on Mark Twain's famous book about the adventures of young orphan Huckleberry Finn.