Operating in Tokyo as a sweeper, Hayato Ijuin, known professionally as Falcon (derived from "Haya" in Hayato), first crossed paths with Ryo Saeba during Central American military conflicts. Initially adversaries, they forged a mutual respect that established their enduring association. Ryo bestowed the nickname "Umibōzu" ("sea monk") due to Hayato's imposing physical presence: tall, muscular, with a shaved head and signature dark sunglasses.

Specializing in heavy weaponry like bazookas and machine guns, though favoring the Smith & Wesson Model 29.44 Magnum revolver for direct engagements, Umibōzu excels in guerrilla tactics, trap-setting, and demolitions, making him nearly Ryo's equal in combat. He frequently utilizes vehicles such as the Toyota Land Cruiser for operations.

Personally, he manages the Cat's Eye Café with Miki, a fellow sweeper and former Central American comrade whom he initially trained. After sustaining a severe eye injury resulting in permanent blindness, Miki became his wife. Despite his blindness, he continues running the café and undertaking missions, relying on his honed skills. He exhibits a pronounced fear of cats, particularly kittens, and significant shyness around women, often blushing during interactions.

In *City Hunter The Movie: Angel Dust*, Umibōzu assists Ryo and others in a heist targeting the nanomachine serum Angel Dust Modified (ADM). He provides tactical support during a waterfront confrontation against assassins and the criminal group Union Teope. His complex relationship with Ryo blends rivalry with deep loyalty, exemplified by his lack of resentment over Ryo inadvertently causing his blindness during a conflict, viewing it as an inherent risk of their dangerous profession.