Shinigami Milk♪ ~Dojikko Kyonyuu Shinigami to Eroicha Bonyuu Seikatsu☆~

The protagonist is Shingo, a college student who isn't popular with the ladies. One day, the shinigami RyuRyu accidentally shears off half of his soul.

Now that Shingo is in danger of dying at any moment, he demands RyuRyu lets him have his way with her breasts until all his attachment to this world is gone!
He also wants to make the shinigami pregnant... A sweet time of sex with mother's milk is about to begin.

[From English DLSite]