Mao-chan (陸上防衛隊まおちゃん Rikujō Bōetai Mao-chan — Ground Defense Force! Mao-chan or Earth Defender! Mao-chan) was written by Ken Akamatsu (post-Love Hina, pre-Mahou Sensei Negima!) and illustrated by RAN.What do you do when Japan is under attack by Ridiculously Cute Aliens? Fight back with even cuter kids! It's the story of Mao Onigawara, Misora Tsukishima, and Sylvia Maruyama, three second-graders tasked with protecting Japan's national landmarks from the aliens... and keeping their grandfathers, the heads of the Ground, Air, and Naval Defense Forces, respectively, from fighting with one another about which one is superior, a problem that often gets in the way of their jobs.
Mao-chan provides examples of the following tropes:
Cuteness Proximity: Everyone gets like this whenever the cute aliens show up, which is part of what makes them a threat — it's difficult to defend yourself or the world when you're being distracted by cuteness.
Disproportionate Retribution: The new prime minister was bullied by the heads of the defense forces back in grade school... so he undermines the Defense Corps with a male trio of elementary school children who manage to get to the scene of every alien sighting first. This is because the Prime Minister's lackeys are sabotaging the girls. ..and also because the aliens aren't real.
Kagome-sensei looks an awful lot like Naru, especially in Chapter 8, when she's not wearing her glasses and has her hair down... and is wearing the exact same outfit Naru was wearing in volume 7 of the manga. No, seriously, it's exactly the same.
There's also a one-shot appearance by a very obvious Keitarō expy. Like, so thinly disguised you'd think they were Writing Around Trademarks. Unlike the real Keitarō, "Keinosuke" failed the fourth attempt at getting into Tokyo U, though.
Heel-Face Turn: After Chinami and Yuriko get captured by their bosses as punishment for their failures, Chinami decides to try to help Yuriko to escape and live a normal life, as she is really a good person. Yuriko insists that Chinami come along, too, and both of them join the forces of Japan in fighting off the aliens.
Honesty Is the Best Policy: The commanders knew all along that the girls had gone to Hokkaido, and Mao-chan's honesty keeps her from getting punished.
Hot Springs Episode: At a run-down place that looks an awful lot like Hinata-sou. Complete with Narusegawa Naru, although they aren't specifically named.
Killer Rabbit: all of the aliens are extremely cute. The "Chief of Operations" turns out to be like this as well, and less than a foot tall. And then there was the "legendary alien that can't be controlled or tamed", Omega...which turns out to be Mao's lost cat Mi-kun.
Monster Protection Racket: The new Prime Minister, to promote his "Three Aces" team. Turns into a game of Zany Scheme Chicken when the Defense Force leaders launch their own fake alien at the same time to try to get the Defense Corps girls back in the public's good graces and independently, Yuriko launches a real alien for the girls to fight... and all three aliens look like pandas.
Omake: Two: One that takes place 10 years later, and then a "summer vacation special" after the higher-ups had been introduced.
Transformation Trinket: The smiling clover pins. Unusual in that the Defense Forces obtained them from the enemy.
Verbal Tic: Misora ends her lines with arimasu, which is translated as "don'tcha know" and "if you please", while Sylvia's casual manner of speech is translated with the liberal use of "yo" and calling everyone "dude/dudette".
What Measure Is a Non-Cute?: This trope is exactly why the aliens are so tough to take down, and why the military has to use a special force of 8-year-olds to accomplish the task.
Winged Humanoid: Misora when she transforms. Justified as her plane doesn't have a cockpit, so she needs something to help her fly.
X Meets Y: Let's see, this series is about a group of politicians and grizzled military types who recruit three children to battle against strange creatures that have come from outer space to threaten the safety of Japan. And they do so using technology stolen from the enemy, and with much destruction of the scenery. Yeah, it's sort of like if Neon Genesis Evangelion were put under the Moeification ray.