To be honest, I have no idea what this anime was about. I think that the best way to summarize it would be that this is a confusing story about angsty elementary schoolers who nearly die. At first, it looks like a generic, wacky anime about moe little girls who have adventures and protect their school from aliens, but it isn't. It was traumatizing, gory shit right there. You probably shouldn't watch this until you live on your own and know to cook... and then maybe you just still shouldn't watch it.
The following information contains spoilers about the whole four episodes so in case you intend to watch this (and I highly recommend you don't unless... you are into this kind of... stuff), you might not want to read the following.
It starts off with the protagonist being elected by a very cruel class, to be an alien fighter. She doesn't want to do it, but nearly everyone selects her anyway. The most likely explaination is that her whole class consists of bullies who conspired beforehand to make her do it.
The other two members of her team are a girl who is apparently brilliant at everything and whose dialogue consists of "nyaa!" and a girl who is very responsible and mature for her age, who is dead sick of doing things for other people. Lovely! They all get cute frog-like aliens to wear on their heads, that will protect them from danger.
The three of them fight aliens together, trying to not kill them in the process but instead giving them a sedative and then capturing them. Or well, I should say, the two of them, as our protagonist herself is terrified of aliens, and prefers to just make herself as small as possible when she sees one, to then burst into tears, hysterically screaming that she is afraid.
Even larger spoilers from here on: it appears that the teacher herself is the one setting out the aliens, ordering them online, to then make the elementary schoolers capture them. Apparently, there is a larger purpose behind the girls chasing monsters, but we never learn it in the entire anime. She is apparently also the one who thought it would be a great idea to give three of her students mind-controlling aliens who would go after the girls. More disturbing yet, the boys who get these aliens are hooked on them and decide to go put them on again after they are captured like the junkies they are. Lovely, teacher, lovely. And when the protagonist's protective alien is brutally killed because of this, after which she goes on an angsty killing spree which will traumatize her for life, slaughtering all aliens including the protective frog hats, the protagonist gets scolded for killing them. Lovely, teacher, lovely.
Meanwhile, the protagonist is dead scared, gains reocurring nightmares of all of the traumatic events she went through, obtains withdrawal symptoms, wants to quit school or at the very least the alien brigade, which is denied to her, her mother is not understanding at all and, even though it was clear from the very start that she was never fit to do this, her teacher does not at some point think it would be a good idea for her to quit, before, say, she becomes insane. Or depressed and suicidal.
Then the situation gets out of hand (if it had not already), by a non-ordered alien appearing on the school grounds and making use of the mentally most screwed up alien fighter girl by convincing her it is her brother dear. It causes momentarily insanity within the other two girls and the teachers, and nyaa! to attempt and murder her friends in a surreal creepy scene.
The anime ends there, but doesn't leave it at that, a highly questionable event still occurs in the credits and it doesn't look pretty.
Basically, why would you do that?