Phineas and Ferb are thinking about the Keronian invaders that came a few episodes ago. As that happens, Perry gets a call that somehow, Pokemon are really raining down on the city while more Keronians are invading, starting with the Keroro platoon, then others. Karara comes for no apperent reason, while people are forgetting what show this is, though when ever they wonder, the theme song plays a bit.
Keroro teams up with Doofenschimecests. Cause he changed his name to make it more evilish. Tamama is heart broken, and teams up with Perry so they can separate this dangerous duo. And RHF was kidnapped. They somehow fail, even with their awesomeness combined, cuteness, and coolness. Doofenschimecestes and Keroro take over the new Earth, or Doofeon. Somehow, Phineas and Ferb save the day by creating more jelousy than ever before in Tamama's heart. In spite of being jealous at a lot of things. He blasts Doof into space, landing on a now deserted Keron.
Keroro was being brainwashed, that's why He actually worked at doing something. The Kerons leave, all but Tamama and Keroro, 'cause their ship was broken beyond repair. Then, out of all that randomness, Ferb and Phineas's mom let them keep them. Ferb got Tamama and Phineas got Keroro. It was very random, but everything was ok. Oh, and somehow, on Keron, Doof turned into a Keronian. They also find out that somehow they are on Keron though they try to get back, but they have turned in to Keronian tadpoles, like Tamama. As they try to look for a cure, they are mistaken as soldiers in the rank of private 3rd class and shipped off for the Keroro platoon. But they are separated, and Ferb goes to the Garuru platoon, the Keroro platoons number 1 enemy.
They are forced to fight each other, but Candace, stops them as they were about to use their final deathblow, sacrificing her life for a few moments before everyone saw the error of their ways and brang her back to life using a special move only used by 2 platoons. They stay Keronians for 11 years before they could go back home to earth. It showed that it was only 11 months to them on earth. So they say farwell to the Keronians and leave.
The whole episode is a secret one found only on DVD.