What anime series follows Gabimaru the Hollow, a ninja sentenced to death, as he seeks the elixir of immortality on the dangerous island of Shinsenkyo to earn his freedom?

The anime series that perfectly matches this description is Hell's Paradise (Review). It chronicles the perilous journey of Gabimaru the Hollow, a formidable ninja from the Iwagakure village, who has been condemned to death. Despite numerous execution attempts, Gabimaru proves to be unkillable, his subconscious desire to return to his wife keeping him alive. Offered a chance at a full pardon by the Shogunate, he accepts the daunting mission: to venture to the mythical and dangerous island of Shinsenkyo and retrieve the legendary Elixir of Life.

Set in the Edo period of Japan, "Hell's Paradise (Review)" plunges Gabimaru and a group of other death row convicts, each accompanied by an executioner from the Yamada Asaemon clan, into a nightmarish battle royale on Shinsenkyo. The island, often referred to as "Paradise" or even "Kotaku," is a deceptive land of both breathtaking beauty and grotesque horror, teeming with bizarre creatures, mutated flora, and immortal entities. The series explores profound themes such as redemption, the fluidity of morality, and the true meaning of life and death, as Gabimaru, initially perceived as an emotionless killer, grapples with his past and rediscovers his humanity through his unwavering love for his wife and the bonds he forms with his fellow travelers.

Yuji Kaku, the creator of the "Hell's Paradise: Jigokuraku" manga, began serializing the series on Shueisha's Shōnen Jump+ app in 2018, quickly gaining a dedicated following for its unique art style and mature storytelling. The anime adaptation, produced by Studio MAPPA, known for its high-quality animation in series like Jujutsu Kaisen (Review) and "Chainsaw Man," brings the manga's dark fantasy world to life with stunning visuals and intense action. The narrative masterfully blends elements of action, dark fantasy, psychological thriller, and survival horror, making it a compelling and often philosophical exploration of human nature under extreme duress.