The Shut-Ins are Mocking My Youthful Day

Hikikomori-tachi ni Ore no Seishun ga Honrou Sareteiru centers around Haruya Aoi, who was bullied as a kid, but helped by Shihane Mizudori, who intimidated everybody. Eventually Haruya had to move away, and they were separated. Six years later, in high school, Haruya moves back to the neighborhood, and meets Shihane, but finds that she has become a shut-in.

(Source: Anime News Network)