The story is fucked up:
It's an alternative universe where Eren have failed to save Mikasa and where he became a member of the Military police. He find her in a whorehouse with fat ugly dudes and get pregnant in front of Eren and then she is giving birth to a baby again because 5 years ago she was raped by the kidnapper and his friends and she start to enjoy this. Back to the image below, she have sex JUST after giving birth to the baby and he is drinking Mikasa's milk while she is drinking semen. She's getting pregnant for tenth time and she is happy that she was not saved with Eren still looking horrified. The doujin ended with a message:
"That was the end of Eren Eager. And probably, the end of the humanity as well."
Source: shingeki no kyojin noa c82