Saigo no Negai: Last pray

A year after getting hit by a drunk driver, Shun feels guilty that his mother died in order to save his life. But since the accident, Shun has been able to see and talk to ghosts. One day Shun meets the ghost of a little girl and then, a little later, meets a suspicion man who wants Shun to act as a medium for that girl. What is the suspicion man after? And will Shun and Shun's father be able to deal with Shun's guilty feelings about his mother's death.