Bokura no 7-kakan Sensou

The story is set in 2020. Mamoru, an indoorsy second-year high school student, has a crush on Aya, the pretty girl who lives next door. However, Aya is moving out due to adult reasons. Not wanting to be separated from her, Mamoru musters up his courage and proposes a plan to run away from home.

(Source: Kadokawa, translated)