Ryuichi Gojiyama

Nobody ever sees the man underneath. Every panel featuring Ryuichi shows him mid transformation, towering fifteen meters as a scaled, dinosaur-like monster built in the mold of Godzilla.

The manga draws him as a bipedal theropod with the anatomy of a carnivorous dinosaur, closest to a Tyrannosaurus rex: jagged spikes marching down the back and along the tail, horns riding the snout, digitigrade legs ending in heavy three-toed feet, a posture tipped slightly toward horizontal, a broad rounded maw, and clawed fingers that push the design toward the TriStar version of the monster known as Zilla. The anime reworks him in solid grey with proportions closer to a human, giving him a rounded snout, four toes, an upright stance, and arms and hands that read as recognizably human, landing him nearer his inspiration. Trigger leaves its mark on his tongue, blackening it entirely in the manga while the anime discolors only the tip, matching how the drug shows on other users.

There is little person left to read. Saturated with Trigger, Ryuichi could not hold a coherent thought and behaved as an animal instead of a man, rampaging through the city and flattening buildings without any apparent aim.

His Quirk, Kaiju, turns him into an enormous dinosaur-like beast. What it does under normal conditions has never been established, since the series only ever shows it while Trigger is in his system. What is confirmed is the scale: he swells to enormous height, his strength and endurance both climb, and whatever mind he has gives way to the animal.

Where Ryuichi came from was never explained; he simply turned up in the city. Kuin Hachisuka is the one who forced the change, and the resulting monster laid into Naruhata, wrecking buildings and battering the Marukane Department Store. Christopher Skyline happened to be the closest Pro Hero and took the fight himself, landing repeated blows until the creature toppled into the surrounding buildings. He was taken into custody soon after, having apparently reverted to human form.