Azusa

Chapter 1-2: Love Letter
Based on a true story about two teenagers Anazawa Toshio and Chieko fall in love during the events of World War II. Toshio enlists into special unit known as kamikaze and he writes one last letter to her before mission.

Chapter 3: Half & Half
Shinichi Nagakawa and Yuuki Sanada are both involved in an accident and die together. But they're given a chance to live again. God lets them live for seven more days. But the catch is that after the time limit, one of them must die again. There's more. God decrees that their lives will be shared, including emotions (guilt) and physical sensations (pain). They are told not to leave the other's side, else both of them die. What will happen during those seven days?

Chapter 4: Azusa
The last one-shot manga in Seo Kouji's Love Letter tankoubon.