, also known in English as Monster #8, is a Japanese web manga series written and illustrated by Naoya Matsumoto. It was serialized on Shueisha's Shōnen Jump+ app and website from July 2020 to July 2025, with its chapters collected in 16 volumes. Shueisha has also published the series digitally on its Manga Plus platform in English and several other languages. Viz Media began publishing the series digitally in August 2020 and has published the series in print in North America since December 2021.
The story follows Kafka Hibino who, after ingesting a parasitic creature, gains the ability to turn into a and now must navigate using his power while trying to become part of an organization that eliminates kaiju to fulfill a promise he made with a childhood friend. Matsumoto wrote the outline of the story of Kaiju No. 8 near the end of 2018 making it his second series for the magazine. The series was heavily influenced by Japanese media, especially Ultraman, while the author's struggles in the manga industry served as a basis for the main character's backstory.
An anime television series adaptation produced by Production I.G aired from April to June 2024, with a second season aired from July to September 2025. A "conclusion arc" to the anime series has been announced. The series has spawned a light novel, two spin-off manga series, and a video game.
By September 2025, the manga had over 19 million copies in circulation. The series has been praised for its premise, characters, and art. The series won the Next Manga Award in the web manga category in 2021 and was nominated for the Eisner Award in 2022.
Synopsis Setting Kaiju No. 8 is set in a world in which monsters named 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 .
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 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.
Production
Naoya Matsumoto began his career in 2006 with Neko Romancer, published in Jump Giga (then known as Akamaru Jump). He authored Nekowappa!, which debuted in Shueisha's Weekly Shōnen Jump in 2009. The series continued a one-shot from the JG1 One-Shot festival. He published another one-shot, Shikai Enbu, in the 2012 spring edition of Jump Giga (then Jump Next), before starting his second serialization, Pochi Kuro, on Shueisha's Shōnen Jump+ website and application in 2014.
Near the end of 2018, Matsumoto presented the initial story idea and outline for Kaiju No. 8 to Shōnen Jump+ deputy editor-in-chief Seijiro Nakaji. Influenced by media such as the Ultraman series—particularly Ultraseven (1967)—as well as Shin Godzilla (2016) and Pacific Rim (2013), Matsumoto aimed to create a story about a protagonist who pursues a goal while concealing their identity from a hostile organization they have joined, which he considered an entertaining concept. The premise of Kafka joining the Defense Force to fulfill his dreams was established early in development, though initial plans involved him maintaining a secret identity while living a normal life. Kafka's predicament was partly inspired by Matsumoto's own career struggles in the manga industry. Working on Kaiju No. 8 was challenging for Matsumoto but allowed him to depart from his typical stories; Nakaji noted the concept was unexpected, as Matsumoto had previously authored fantasy series.
The page layouts were designed for clarity, particularly on smartphones, due to the manga's digital release. Nakaji cited a fully colored panel in the second chapter as an example of utilizing the digital format in a way not feasible in a physical magazine. A coworker suggested the kaiju codenames be based on typhoon categorization to enhance their portrayal as disasters. The kaiju designs drew from mythological creatures, animals, and plants. Kaiju No. 8's design was modeled after , with its color scheme inspired by the film Tron (1982).
Matsumoto worked with three assistants: Osamu Koiwai, responsible for background art; Jiro Sakura, who handled finishing work; and Mantohihi Binta, credited with weapon design. For background art, Matsumoto provided a storyboard with panel compositions to Koiwai, who created a draft for approval before finalizing the art, a process taking three to four days. Koiwai shared his creative process for the series on YouTube.
In August 2020, Kaiju No. 8 adopted a schedule of three weekly chapters followed by a one-week break. From June 25, 2021, the series switched to a biweekly schedule.
Anime adaptation Production I.G producer Masashi Ohira brought Tetsuya Nishio onto the project as character designer and chief animation director, believing Nishio's designs facilitated animation and possessed a three-dimensional quality. Nishio designed the human characters and humanoid kaiju. In addition to serving as chief kaiju designer, Mahiro Maeda provided detailed imagery of kaiju anatomy for battle scenes. Ohira recruited Shinji Kimura as art director for his ability to create a realistic setting. Toho Animation producer Katsuhiro Takei stated that Production I.G and studio Khara were selected due to similarities between Kaiju No. 8 and their previous works. He noted the series' focus on daily life resembled Production I.G's Patlabor (1989), while its setting evoked Khara's Neon Genesis Evangelion (1995). Involving both studios aimed to recreate the aesthetic of 1990s anime.
The anime combined hand-drawn and 3D animation. Lead 3D animation director Masaru Matsumoto worked with a small team using Autodesk 3ds Max and Blender; production began in March 2022 and continued during the broadcast. Directors Tomomi Kamiya and Shigeyuki Miya identified sequences requiring 3D animation during storyboarding, while Kimura and mechanical designer Shinobu Tsuneki collaborated with the team to evoke the aesthetics of Production I.G films like Patlabor and Ghost in the Shell (1995), emphasizing realistic military combat. Extensive 3D animation was used for battles against numerous monsters and for dynamic camera work in action sequences. Studio Khara, in collaboration with the creative agency WOW, produced the opening sequence. Directed by Hibiki Yoshizaki with Kouhei Nakama as CG director, the sequence aimed to depict the origin of the .
Media Manga
Written and illustrated by Naoya Matsumoto, Kaiju No. 8 started on Shueisha's Shōnen Jump+ app and website on July 3, 2020. The series ended with the release of its 129th chapter on July 18, 2025. Shueisha has collected its chapters into individual volumes. The first volume was released on December 4, 2020; a promotional video for the volume, presented as a news program, was shown on the big screen of Yunika Vision at Seibu-Shinjuku Station from December 4–10, 2020. The 16th and final volume was released on September 4, 2025.