Sgt. Frog Episode 189: Dororo, Assassin From the Past
Episode 189 of 358 of Sgt. Frog, aired December 1, 2007, 25 minutes. Available with English subtitles and dub where released.
Episode summary
Captain Jirara, Dororo`s former superior officer, has gone AWOL from the Keron Army. Dororo has a suspicion that Captain Jirara is somewhere on Earth, but facing him will require Dororo facing up to his dark past as an assassin in their former platoon. Source: crunchyroll