Maou ga Gendai Sekai ni Tensei Shitara Oppai o Medenakute wa Naranaku Natta Ken

After losing in the final battle against the Hero, the Demon King is reincarnated into the modern world.
However, even after reincarnating, the curse cast by the hero's was not dispelled.

"You shall not harm 'beings weaker than yourself'".
"You must show compassion to such beings at least once a day".
Disobeying these commands causes him terrible pain from the hero's curse mark on his chest.

Before the final battle with the hero, loving the lowest class of monster in the other world, the slimes, he would make the curse subside each.

However, in this other world where he has reincarnated there are no slimes or any other monster.
When the daily time limit arrived the Demon King started clutching his chest in agony.
Finally he collapsed in front of three sister who live in this other world.

However, that night...
Someone was huddling around the bed of the suffering Demon King.
When he reached to touch them with his trembling hand it felt soft and warm.

"A slime...?"

The demon lord gave his love those soft and elastic beings... "Boobs"!
He didn't know the three sisters they belonged to, but he lost himself in rubbing, grabbing, stroking and sucking those things in his hands.
In response to the rough treatment, the owner of that soft fair skin answered with sweet moans.
Then, his pain gradually faded and the feeling of ejaculation raised instead...

[Translated from DMM]