Kaiju No. 8

=== Setting ===
Kaiju No. 8 is set in a world in which monsters named kaiju regularly cause disasters. Japan has the highest rate of kaiju attacks in the world, therefore in order to combat them it establishes the Japanese Anti-Kaiju Defense Force (JAKDF). Kaiju are assigned a "fortitude level"—a scale indicating their overall strength, and are classified as honju—more dangerous, stronger kaiju, and yoju—smaller kaiju that can accompany or sprout off from honju. Kaiju that have high fortitude levels or abnormal characteristics are given a number as an identifier based on when they first appear, and are classified as daikaiju.
Defense Force officers wear powered suits made from kaiju remains that grant them increased strength, speed, and durability. The suits have a total power output, measured in the form of a percentage (referred to as "unleashed combat power"), which varies from person to person (depending on their ability), with a maximum of 100%. The suits also influence how strong an officer's weapons are.
Daikaiju remains are used to create stronger weapons named Numbers (ナンバーズ, Nanbāzu) that are named after the daikaiju they are made from, but only a select few can use them if they are deemed compatible. Numbers weapons are much stronger than regular suits and provide their users with special abilities. The Defense Force consists of field officers led by platoon leaders, with varying levels of unleashed combat power, and captains and vice-captains whose combat power exceeds 90% and who lead divisions. Field officers are supported by a team of operators who provide information on kaiju, and monitor the field officers' health and suit output.

Plot

Following the destruction of their hometown by a kaiju, childhood friends Kafka Hibino and Mina Ashiro vow to join the Japanese Anti-Kaiju Defense Force. Mina ascends to become captain of the Third Division, renowned for her uniquely destructive marksmanship, while Kafka repeatedly fails the entrance exam and works on a cleanup crew disposing of kaiju remains. His resolve is renewed upon meeting Reno Ichikawa, a young coworker and fellow aspirant to the Defense Force. A parasitic creature subsequently enters Kafka's body, granting him the ability to transform into a humanoid kaiju. Designated "Kaiju No. 8", Kafka escapes military custody and enlists in the Defense Force, concealing his powerful alter ego.
Kafka and Reno pass the entrance examination and are assigned to the Third Division alongside Kikoru Shinomiya, a prodigious kaiju slayer. During their first mission, they confront another humanoid kaiju, "Kaiju No. 9", which Kafka fails to eliminate. He is later forced to reveal his kaiju form to save the Tachikawa base from destruction during an attack by "Kaiju No. 10". Apprehended by Mina, Kafka is taken to Defense Force headquarters. He proves his value by defeating the Director General, Isao Shinomiya, in a duel. Kafka and Kikoru are then transferred to the First Division, led by Captain Gen Narumi.
No. 9 attacks Shinagawa, and while two of its duplicates are destroyed, the genuine entity confronts and absorbs Isao Shinomiya, acquiring his Numbers 2 weapon, a powered suit of armor derived from Kaiju No. 2. Empowered, No. 9 escapes to prepare a full-scale invasion of Japan. In preparation, Kafka and Kikoru undergo intensive training; Kikoru inherits her mother's Numbers 4 weapon, while Reno acquires the Numbers 6 weapon and trains with the Fourth Division. During his own training with Vice-Captain Soshiro Hoshina at a shrine commemorating kaiju slayers of the Meireki era, Kafka perceives a spectral vision of an ancient warrior.
Months later, the invasion begins with kaiju designated Nos. 11 through 15 attacking specific Defense Force members. Gen, Soshiro, Kafka, and Kikoru defeat their assigned opponents, with Mina being the last to prevail. No. 9 uses the corpse of Kaiju No. 14 to teleport to Mina's location, intending to kill and absorb her to acquire her destructive power. Kafka reaches her in time with Reno's assistance. Together, Kafka and Mina defeat No. 9, but its corpse mortally wounds Kafka and is subsequently taken over by an ancient, powerful kaiju from the Meireki era that it had absorbed. This entity, Meireki, easily overpowers the remaining defenders.
The larval kaiju manifests in Kafka's mind and reveals it is a parasitic core born from the warriors Meireki slew, who were also responsible for the Great Fire of Meireki (and thus the spirit he saw earlier). Saddened by the turn of events, it offers Kafka a choice: restoration of his human heart or transformation into a new core, permanently reviving him as Kaiju No. 8. Choosing to fight, Kafka revives as a Kaiju in a stronger form and, alongside Soshiro and Gen, confronts Meireki, who resurrects previous kaiju to battle them. Kafka, Kikoru, and Mina ultimately defeat Meireki, with Kafka delivering the final blow. After the battle, Kafka's health deteriorates, but he recovers from a four-month coma. His heart is restored by the spirit of Isao Shinomiya, who entrusts him with the future.
He returns to active duty at the Tachikawa base, welcomed by his comrades. A year later, Kikoru is promoted to vice-captain of the First Division, and Kafka is appointed platoon leader of the Third Division in recognition of his service. The Defense Force permits him to use his kaiju form when necessary, provided he exercises caution to remain undetected.