If you liked the Alien Nine anime, the Anime-Planet community thinks you'd like:
Japan, present day: Alien Invaders are everywhere, taking over peoples' bodies. Fighting them is Isuzu Ayane, an introverted young girl with the ability to control powerful dimensional Gates. Under the guidance of Kageyama Reiji, a mysterious businessman, she battles Invaders and recruits new Gate Keepers. Will she and her new comrades be able to save the earth?
Do you like young girls battling endless waves of weird-looking aliens? Do you care if one of the main characters is a bit whiny and hates her job as alien hunter? Then these animes are for you. While the animes differ in how the girls' powers are obtained, they still share the motif of child soldiers.
Strange things have been happening at a local high school... mysterious disappearances, strange powers and brutal murders all emerge amongst kids who, up till now, have been perfectly normal. Even the Shinigami (Angel of Death) herself has been sighted. What's happening? The answers lie in the mysterious creature known as Boogiepop...
In a futuristic world, the virtual world is merely a layer on top of reality; within it, cyberpets are abundant and information is plentiful, and it is only visible by wearing special cyberglasses. In Daikoku City, this cyberspace is behaving strangely: cyberpets are going missing, dark entities known as "the Illegal" roam obsolete space that shouldn’t exist, and a large pink antivirus program known as Satchii wanders the streets, attacking both virus and pets alike. Sixth grader Yuko Okonogi has just moved to Daikoku City, and after cyberdetective children help her rescue her lost dog, she soon joins the others in a search for the truth behind these strange occurances.
The story is quite different, here you have aliens and there you have internet environment, but I found the characters someway similar, not only because they're children but also the atmosphere of children facing something bigger than themselves.
Haré and his mother live peacefully in the jungle, until one day the boy is overtaken by a omnipotent shadow. Later, he awakens to find Guu, a strange girl with even stranger abilities - notably, the ability to switch from a cute, lovable Guu, to a menacing delinquent who eats everything. Now Haré must live with Guu, and lead a normal life, despite her oddities.
Like Alien Nine, Hare+Guu is another show that is fairly random and odd. It is very different, but incredibly funny. It has one character who is extremely odd, as well as some strange jungle creatures.
In the year 20XX, insects have developed immunity to every kind of insect spray. To counter the incredible rise in insect numbers the Japanese government developed tiny extermination robots code named "Hoihoi-san". The popularity of Hoihoi-san units rises not only as a night time extermination unit, but for doll collectors as well! However, when a rival company introduces its own tiny extermination robots a new form of corporate sabotage begins, as they target not only the insects, but all Hoihoi-san units themselves!