Un:Birthday Song ~Ai wo Utau Shinigami~

Hotori is your average high school student – except that she has 1 month left until her death. Two shinigami are sent down to earth have 1 month to watch over her and make sure she has no regrets left so she can descend into the after life. The two shinigami are Zen and Rikka, and if their mission succeeds, they will get a get out of hell free coupon to be reborn again. If they fail, they will be stuck doing shinigami work for all of eternity. Hotori starts to think about how to live her life to the fullest in the remaining time she has left, and one of the things on her bucket list is to confess to her crush Shizuru.

Résumé

Kanno Hotori was a normal girl leading a normal life. One day, out of the blue, two unfamiliar guys appear before her. The strangely-dressed guys informed her:

'You only have one month left to live'.

Calling themselves 'Reapers', they had come to inform Hotori that the end of her life was drawing near. Having to obey the fate that came upon her, she had to give the Reapers her soul. However, just before she did so, Hotori had a wish she wanted granted dearly.
That wish was to tell her one-sided crush that she loves him.