Ushiro No Shindere-San

From Manga Updates Karugasaki Tora decided to repeat a grade and turn into a delinquent just so he could be popular, on his best friends advice. However, his plan backfired and nobody talks to him in his new classroom. The only thing he can look forward to is seeing the cute girl sitting next to him, but after trying to talk to her she immediately kicked him and threw him out the window. Later the same day, though, he saved her and a little girl from being hit by a truck. No longer able to avoid him, the girl reveals that she's a ghost playing a shinigami's game. She must get the boy she likes to return her feelings at times given by a pair of hourglasses so she can return to life, or fail and be sent to hell together. Unfortunately, her feelings have awakened for Karugasaki...