Rikujou Bouei-tai Mao-chan

It's practically the same anime, Mao-chan is just less serious and more focused on overall cuteness. In story: Both are about a group of little girls who transform into marching band style uniforms to fighting off aliens in a city by the ocean with the support of the military. In characters: Mao is similar to Akane, they're both the main characters and they both receive their powers from their grandfather. Aoi and Misora are almost the exact same character, they both already have established friendships with the main characters and are the second to receive their powers. Kagome Mishima and Mizuha Amagi are both women in the military who get assigned to be the school teacher for the main characters.  read more 

Alien Nine has the same theme of grade-schoolers capturing aliens but with a more serious and slightly darker storyline. 

Cute girls in semi-shitpost military setting. That's it. 

Both have the same plot, but Mao-chan is more ironic and actually make you laugh like a creep. 

The anime are both by the same creator (Ken Akamatsu) and have the same character designs. The anime don't really have much in common aside from that. But there are some cameos and references to Love Hina in Mao-chan, which can make it more fun.