Futaba's longest running and most popular series really starts here (milk fetish is kind of a prequel). It's pretty easy to see why this series got so popular with its unique art style, lots of futa on futa sex, and a fun story to carry it along the way.
Another great entry in the Futaba Yodomu multiverse
In this story we see how the girl from Milk Fetish and the doctor from Futanari Check-Up first met. Chronologically it takes place after Milk Fetish and before Futanari Check-Up.
So I guess it turns out this girl from Milk Fetish is actually a succubus and she is having a medical emergency due to not ingesting enough futa cum. The doctor in this story treats her well and well, a girl who can not only take the pent up urges of many futanari girls visiting the clinics but also NEEDS to take it as a succubus, she'll be an important asset to the clinic. Make sure to gulp down all that cum and don't waste a drop!