From mangaupdates:

Hayama Makoto is tormented by sightings of shinigami*, Asano Mitsuki dwells on his dead sister’s shadow, and Koumoto Yaeko longs for the love of her life―these are the heart-rending yet tender tales of the people whose thoughts dwell on life and death, and of the white Shinigami Momo.

*Shinigami (死神) is a figure in Japanese culture responsible for collecting the souls of the dead, and literally translates to "god of death."