Koikoi 7 (2002)

Tanaka Tetsurou is just your normal high school student, except he’s been in the hospital for a few months and missed one month of school. On his first day back he’s saved from a car accident by a girl who looks just like someone he used to know. This girl, Asuka Yayoi, soon introduces Tetsurou to her friends and they begin living together. Thus begins a whole new life for Tetsurou filled with school, romance.....and giant robots. But all is not as peacefull as it seams, because the girls don’t seem to be at all normal. Throw in another Asuka Yayoi, a mysterious plot by Tetsurou’s father, and new medical technology that promises immortality and this soft-hearted school story becomes an action packed battle for the future of Tetsurou and his friends.(Do not be tricked by the first volume of this manga. It gets dark and very serious after the second half of the second volume.)

Source: www.anisearch.com/manga/4116