"Kemama" refers to a four hour-long Skype call between Mugiwara Yoshi and ThornBrain. It predates Thorn's tendency to record their Skype calls and was in-fact the instigator. Kemama eventually found his way into Sgt Frog Abridged in Episode 21.
This made no more sense in-context than it does here
Sometime late-January 2010, shortly after DFatman signed off of Skype, Yoshi and Thorn began roleplaying as their respective versions of Tamama. Due to the explicit nature of their in-character conversations, this spiraled progressively from using glow-sticks as sex toys to Keroro joining in. At one point Yoshi-Tamama's penis explodes, and in the chaos they ask Kululu to fix it. He creates a machine that transforms Tamama into various forms. After several undesirable forms, (one of which is so frightening that Thorn-Tamama tells him to just go back into the machine without describing it), Yoshi-Tamama comes out as a very attractive female. They all have sex, with Kululu watching.
However, because Yoshi-Tamama was a female, she became pregnant with Keroro's child. The child rapidly grows in her, and she is forced to have the child just before she reverts back to being male. The child is a boy with a purple penis shape on his belly, and his first word is also "penis". The child is named Kemama, a portmanteau of Keroro and Tamama.
From that point on, the call progressed into a kind of sitcom, with Keroro being the dad, Tamama's 1 and 2 being tired housewives, and Kemama rapidly growing. Kemama is soon old enough to go to school, which is eventually burned down.
Not much more is remembered about the call, other than that the entire thing lasted roughly four hours.
The "Kemama" call did not affect Sgt Frog Abridged in a direct or significant way until Episode 21, though it is an example of the sexual and ridiculous roleplays Yoshi and Thorn engaged in with the Keroro and Tamama characters early on, and these would shape their personalities and relationship in the lead-up to the series. Their roleplays were based on the December 2009 inside joke, Tamama Tits, which caused their version of Keroro to become interested in Tamama, thus them starting out as a couple in SFA.
The call was also the direct catalyst for Thorn recording all of his Skype calls in the early days, some of which were uploaded to YouTube or used in other ways in the years following. Thorn swears that if time travel is ever developed, he will go back and record the Kemama call.
Kemama finally found his way into SFA as the name of Keroro and Tamama's baby. Tamama's pregnancy, which apparently lasted three years, was first hinted in Episode 18 and was discussed at various points in Ask GiroDoro and the following post-revival episodes. Kemama is born suddenly during the attack on the base by Dokuku, with Tamama firing the baby at him as a missile. Kemama disappears until he turns up unharmed in Keroro's bed later that night.
The Kemama in the episode does not share the ridiculous features of the original Skype call's Kemama, though he does share the rapid growth, becoming an adult and growing massive in the span of two days. This Kemama however was also conceived by Beetle Jesus through Keroro, and his adult form in-turn is a giant Albatross, Eater of Worlds. At the end of the episode, Kemama flies off into space never to return. Tamama also shares the call's Tamama's apathy and inactivity in taking care of Kemama, leaving Keroro to deal with the brunt of parenthood. No school gets burned down, but the Hinata house does get destroyed when Kemama transforms.