From the Keroro Wiki
Aki Hinata's husband (Natsumi and Fuyuki's father) has yet to be seen or mentioned in the Keroro Gunso anime and the manga. The only time he was really ever talked about was in one chapter of the manga, where Fuyuki thinks Natsumi might be jealous of Keroro (because his father was set to visit, though he never showed up) and stated the they never met their dad. No clues have ever been given about him in any of the Keroro Gunso media. He has yet to be seen or mentioned in the metaseries itself.
