Kazuhiko Kai attends Houshou Private High School as a second-year student. His fair skin, green eyes, and shoulder-length hair styled in thick, textured twists resembling dreadlocks create a distinctive look. He is slightly shorter and skinnier than average, often wearing a red button-up shirt over a black undershirt, tan skinny jeans with a silver chain on the belt loops, and brown cowboy boots.

Kazuhiko initially displays a cynical, self-reliant personality, openly criticizing classmates like Atsushi Kamijo and Kasumi Momosaki for perceived pretentiousness. This worldview stems from a past incident where he defended a boy from delinquents but was falsely accused of smoking when the boy refused to corroborate his story. The betrayal cemented his belief in relying solely on oneself. He possesses skills in lock picking, strategic planning, and deception, though his background beyond school remains undefined.

During the island survival ordeal, Kazuhiko prioritizes self-preservation early on, tricking Hiroshi into charging butterflies as a diversion—indirectly causing Hiroshi’s death. He assists the group by breaking into a vending machine for supplies, scavenging detergents to repel insects, and restoring a clinic’s power by activating a generator. He initially lies about unlocking the clinic window to hide his lock-picking ability but confesses when the group faces imminent danger.

A pivotal moment occurs when he intervenes to stop Ryou Usui from raping Mutsumi Oribe, revealing underlying loyalty beneath his detached exterior. His cooperation grows as he helps Mutsumi kill a giant dobsonfly by overloading a light fixture, electrocutes invading crabs using a generator cable, and devises a plan to lure a giant trapdoor spider away by amplifying recorded wasp sounds. This strategy saves Mutsumi but results in Marika Chuujou’s death. During this, Nozomi Aoyama coerces him into sex in exchange for her assistance, which he reluctantly accepts to advance the rescue.

Later, Kazuhiko actively protects the group: urging Kasumi Momosaki to flee firefly larvae, creating a smokescreen with torches to repel giant beetles, and helping load supplies onto a lifeboat during the escape. He prevents Ryoko Shikimori from rushing into danger after Pops’ death and reveals he collected clinic SD cards as evidence for authorities. Interactions with Chitose Naruse challenge his isolationist philosophy, while a moment of levity with Mami Miura about her career struggles further softens his cynicism.

His involvement in sequel media like *Die! The Island of Giant Insects* or spin-offs such as *Mountain of Giant Insects* lacks concrete information in available sources.