- Taylor: "All this time, I thought it was our own people behind this."
- Mei: "A home-brewed Kaiju? Not likely."
- Taylor: "That means the Precursors can make Kaiju that look like us."
- —Taylor and Mei
Kaiju Boy (also known as Boy) is a Human-Kaiju Hybrid created by the Precursors. Discovered in the basement of an recruitment center for the Pan Pacific Defense Corps, he is saved by siblings Taylor and Hayley Travis. Forming a bond with the siblings, he accompanies them on their journey to find their parents.
Unlike previous Human-Kaiju hybrids (created by humans), the boy appears outwardly human, and frail at first glance. In his human form, he possesses superhuman strength, and is strong enough to shatter reinforced glass, or halt the single fist of a Kaiju-Jaeger Hybrid despite his size. His skin cannot be pierced by ordinary weaponry, like firearms.
The boy appears to sustain himself from eating wildlife, but can also ingest human beverages. He does not appear to speak, but can understand what is being said to him. The boy is largely passive towards those he trusts, and will step up to protect them against hostile humans.
If the threat to himself or those he cares about is sufficient enough, the boy's eyes will shift from blue to red in a show of hostility. He has the ability to shed his human persona and, growing considerably, becomes more outwardly Kaiju. In his Kaiju form, the boy's skin toughens and becomes craggy, lined with the bioluminescent glow of his blood. His strength increases considerably, and he is strong enough to take on the likes of a Category IV Kaiju.
Pacific Rim: The Black
Trapped in Meridian City
During the Uprising Wars, the Human-Kaiju Hybrid appeared to have been captured by the PPDC and placed inside of tank within the PPDC Recruitment Center. During a Rogue Kaiju-Jaeger Hybrid's rampage through Meridian City, it picks up on his presence and attempts to establish a Drift with him.
Later, at an undetermined time, when the hybrid regains consciousness inside the tank, he sees Hayley outside and mimics her movement. He watches Hayley try and fail to break tank using a crowbar. Using his own strength, he breaks the tank and promptly loses consciousness. Hayley and Taylor are able to escape from the recruitment center with the hybrid and the power cell from his tank. Unbeknownst to the boy, he and the Travis siblings are pursued by the canine Kaiju roaming the city, and are saved by the other hybrid.
After his first meeting with Apex, Boy continue to follow the Travis siblings to the Clayton City after they found a mayday signal coming from the City. Unknowingly, Mei is also staying at the town, offering them hot chocolate and continuing their journey to find the signal. They eventually come across an abandoned Hunter Vertigo, and he follows them inside the conn-pod.
Boy becomes angry now seeing his friend Hayley lying unconscious, and Taylor risking his life to save them. He suddenly roars and his mouth glows blue, creating an energy orb surrounding himself and Hayley. He transforms into a Kaiju, and attacks Copperhead. He punches Copperhead in the face and manages to get onto the Kaiju's back. Clinging onto Copperhead's scaly back protrusions, Boy rides the Kaiju like a bull. Unfortunately he is flung off, and Copperhead gains the upperhand flinging him into a pile of debris, Boy gets stuck under the debris and growls in frustration. Hayley who has regain her consciousness approaches him and attempts to soothe him. However Copperhead comes from behind them and attempts to crush them but is intervened by Atlas Destroyer who is being piloted by Mei and Taylor. Hayley realizes she can help as well and flees from Boy to go dislodge the nuke from an inactive Hunter Vertigo.
After defeating Copperhead Hayley, Taylor, and Mei come back to the Kaiju transformed Boy. They discuss how he was created and decide he was made by the Precursors to appear as a human.
- Kaiju Boy's name is spelled "Kaiju bOy" in the credits of for "Showdown". The official soundtrack, composed by Brandon Campbell, also contains a track titled "b0y". Showrunner, Craig Kyle also spells the name "bOy".
- Kaiju Boy's ability to transform into a Kaiju is akin to that Eren Jaeger's (and other titan shifters') ability to transform into a Titan in Attack on Titan.