Alien Nine

The story begins when high school student Kazuki Muto is killed one night saving a mysterious girl from a monster, only to wake up in his school dorm, believing it to have been a dream; however, he soon finds out that dream wasn't a dream at all when a giant serpentine monster attacks him and his sister. Tokiko Tsumura, the girl he saved, explains that the monster is a homunculus. Kazuki had been attacked and killed by it when he was rescuing her; however, she, feeling responsible for him, revived him by placing a Kakugane medallion in his chest, serving as a replacement heart.

To gain the skills he needs to surpass his powerful father, Baki enters Arizona State Prison to take on the notorious inmate known as Mr. Unchained.

Shy Natsu awakens as part of a group chosen to ensure the survival of humanity. Together, they have to survive on a changed Earth.

As a prophecy of doom unfolds on the peaceful land of Britannia, a purehearted boy sets out on a journey of discovery — and revenge.