Mahoutsukai Tai!

Magic User's Club (魔法使いTai!, Mahō Tsukai Tai!) is a Japanese OVA series released in 1996, followed by a 13-episode TV series in 1999, which was broadcast by WOWOW in Japan, and later released in North America by Media Blasters. The manga adaptation was split into two themes, a shōjo manga version by Tammy Ohta and a shōnen manga version by Shamneko.

Plot
One sunny day invaders came from space. They weren't little green men or funny girls wearing school uniforms, though. They were ugly robots which defeated the UN forces in seconds. After that, the invaders roamed around peacefully (unless attacked) and observed human society with politeness. Still, they were aliens and the people of Earth wanted them to go home. Thus, the Kitanohashi High School Magic Club took it upon themselves to defeat these foul robots and free the world.

Other Sources

 * (Anime)