"Animal 1" is a science fiction anime series set in a dystopian future where humanity faces extinction due to a mysterious virus that transforms humans into monstrous creatures known as "Beasts." The story centers on a group of genetically enhanced individuals called "Hunters," who are humanity's last line of defense against the Beasts. These Hunters are equipped with advanced technology and unique abilities derived from animal DNA, allowing them to combat the increasingly powerful and intelligent Beasts.

The protagonist, Kaito, is a young Hunter who struggles with the moral implications of his role. His DNA is spliced with that of a wolf, granting him heightened senses, agility, and strength, but also causing him to question his humanity. Kaito is joined by a diverse team of Hunters, each with their own animal-based enhancements and personal motivations. Among them are Aya, a stoic and strategic leader with feline traits; Ren, a hot-headed and impulsive fighter with reptilian abilities; and Sora, a compassionate medic with avian enhancements. Together, they navigate a world where trust is scarce, and survival often comes at a cost.

The narrative unfolds as the Hunters uncover the origins of the virus, which is revealed to be a result of unethical human experimentation. As they delve deeper, they encounter a shadowy organization responsible for both the virus and the creation of the Hunters. This organization seeks to control the remaining human population by manipulating the Beasts and the Hunters alike. The series explores themes of identity, morality, and the consequences of playing god with nature.

Throughout the series, the Hunters face increasingly dangerous Beasts, each more evolved and intelligent than the last. The tension escalates as internal conflicts arise within the group, testing their loyalty and resolve. The climax involves a confrontation with the organization's leader, who reveals a chilling plan to reshape humanity into a new species. The series concludes with a bittersweet resolution, leaving room for potential future developments while tying up key narrative threads.