Kanojo-tachi no X-Day, Houkago Hokenshitsu Recommendations
X-Day and After School Nightmare are both titles by the same author. Therefore, the art and "feel" is similar. The characters of both series are tragically drawn, conflicted with themselves, and interesting.
They're both from same mangaka, they have a terrific ending and their characters' psychologies are similar.
Another manga by Mizushiro Setona. It has a crazy plot, serious themes, and a great ending twist.