Chapter 3: Monster

Team Z grinds through a conditioning block of sprint and vertical-jump measurements before breaking for dinner. Most of the squad drifts off to sleep afterward, but Isagi is too keyed up to rest, so he slips out to train alone and runs into Meguru Bachira doing the same.

The two square off in a private duel. When Isagi wonders aloud whether Bachira would ever feed him the ball, Bachira answers that a creature living inside him urged the pass, sensing that Isagi carries a similar beast of his own. Bachira admits he is grateful that Blue Lock brought the pair of them together.

The whole team is then summoned to hear updated standings. Gurimu Igarashi climbs from 300th to 275th, while Isagi rises from 299th to 274th. Ego lays out the facility's design, describing five tiers that hold twenty-five squads labeled from "B" down to "Z," with every group in a given tier housed under identical conditions. Once the earlier game of tag thins the field to 275 survivors, the First Selection is declared open.

Bachira reveals that his instinct-driven football springs from a "monster" he pictures inside himself, and he claims to glimpse the same hunger in Isagi. The cull following the tag game removes one competitor from each of the twenty-five groups, leaving 275 players standing, and Ego signals that the First Selection is about to begin.

"Monster" runs under the Japanese title Kaibutsu and stands as the third chapter overall, collected in Volume 1 within the Introduction Arc. It reached Japanese readers on August 22, 2018 in issue 2018-38 and later saw an English release on March 16, 2021, across twenty-four pages. Its events are adapted in Episode 2 of the anime, and it sits between Chapter 2 and Chapter 4.