Alien Nine is a hell of a trip.
This four-episode OVA presents itself as a cheery slice-of-life series about three 12-year-old girls who travel around school on rollerblades catching aliens that are invading the planet for reasons that are never truly revealed but are vaguely hinted at. There are disturbingly dark underpinnings to the story, though; the anime uses the same cheery veneer — bright colors, simple character designs, bouncy music, etc. — to present scenes such as bonding among the girls, a cleaning/feeding ritual with their Borg partners (the Borg being aliens who attach to the heads of the girls and take part in a symbiotic relationship where the Borg protect the girls against the aliens in exchange for feeding off their sweat) and the brutal slaughter of various alien creatures.
It’s all quite disturbing, and purposefully so. But what the hell are these girls fighting for? (Major spoilers for Alien Nine within. Read at your own caution. Also, all my speculation is directed solely at the OVA, so I can only make sense of what was chosen to be included in it.)