Author: Atsuko Asano
Illustrator: Kino Hinoki
The story is set in “No. 6,” a future model city in 2013. Raised as a top-ranking elite since the age of 2, a boy named Shion lives in an exclusive area in No. 6. On the night of his 12th birthday, he rescues a boy who calls himself “Nezumi” (Rat). Nezumi ran away from the city’s Special Security Area. From that moment on, Shion’s life is changed forever… (Source: MyAnimeList.net)
This manga is one of my very favorites. I love the theme of science fiction and the hint of BL.
This manga is originally a novel of Atsuko Asano, then it also got an anime of the same title, aired on 2011.
Try it, don’t get into you the hint of BL I mentioned, because this is really a good anime. Great story, great characters, and everything in it. 😉