- “If I'm overloyal to the Prowler Corps, and by extension, the UNSC, it is because they rescued me from Hell itself.”— Akio Watanabe
Watanabe served in the ONI Prowler Corps during the Human-Covenant war. He disapproved of using torture as a means of interrogation not only because it was ineffective, but because he had personal experience with it as well: he had scars from insurrectionist torture running from his wrists to his elbows, and he also had scars around his neck. The Prowler Corps rescued him from torture, and thus he became very loyal to them.
In 2535, Watanabe proposed the UNSC Midsummer Night's mission to go to Charybdis IX and track and eliminate the source of smuggled Covenant weaponry. He was, for the most part, disliked by the Midsummer Night's crew due to the fact that he was quiet and secretive, spending most of the journey to Charybdis IX in his personal quarters. He had read the Carver Findings and agreed with them: Watanabe believed that the colonies were a powder keg due to their innumerable cultures and religions, and that a constant war, such as the Insurrection, was inevitable. He often compared the Insurrection to the Rainforest Wars.
After Petty Officer Jeffries' Pelican was shot down over the Scyllion Warehouse District, Watanabe helped Lieutenant Jacob Keyes snap out of his guilt trance and back into reality. Watanabe was killed by insurrectionist Jason Kincaide while defending the crew's extraction point alongside Keyes and ONI agent Captain Corinthia Hansen. His death was avenged by Keyes, who killed Kincade in retaliation.
Watanabe was known for his cold approach toward individuals and for his single-minded focus on his mission. Those treated by him in such a way still felt pangs of sadness when Watanabe died, however.
- Halo: The Cole Protocol (First appearance)