Kaku began his career as an undercover agent embedded in a shipbuilding company, posing as a skilled carpenter to covertly collect intelligence. Trained since youth in stealth tactics and martial arts, he mastered a distinctive combat style wielding four blades with unmatched flexibility and precision. His strategic mind and dry wit proved as sharp as his swords.

A critical mission required infiltrating a city to secure blueprints for an ancient weapon, during which encounters with a pirate crew strained his allegiances. When his government ties were exposed, he engaged in a climactic battle, unleashing newfound zoan-type devil fruit powers that transformed him into a giraffe hybrid. This fusion of animalistic strength and refined swordsmanship elevated his combat prowess.

Post-mission failure led to disciplinary action and exile, during which he reconnected with former allies while evading capture. Eventually reinstated into an elite intelligence unit, he transitioned to overt operations, including diplomatic missions abroad.

Though interactions with past adversaries remained strictly professional, underlying tensions from shared history lingered. His responsibilities grew to encompass intelligence analysis and strategic counsel, adapting seamlessly to shifting political dynamics.