Onedari Milky Pai

Main character lives alone in the apartment after his parents go overseas. He has to take a two week break from his part-time job in the cafe because of forced additional lessons. But as he returns to his part-time job he is amazed to notice that all four waitresses now suddenly have huge breasts thanks to new revolutionary medicine. But the drug has side effect of unstable behavior and milk pouring out unless male semen massage is done. His childhood friend comes to him in tears as she can't return home with such huge breasts. After the shameful procedures her breast shrinks to the normal size. However, part-time job waitresses learn about this efficient cure and demand their share of treatment.

[From vndbreview]