Chichigami-sama no Iutoori!

Houjou Mairi and Fukaya Houko find themselves unknownly blessed by a forgotten fertility goddess, it turned the two into lactating tanks who are constantly in heat; however the girls don't take this is a blessing at all!

In the middle of that there's their classmate and protagonist, Sedou Ikuro; your average pervert teen who has a lactation fetish, he has just found himself in heaven with how Mairi and Houko are acting right now, but still he wants to help so he embarks with them on a quest to find out this Breast Goddess and undo this curse.

Still, the longer Mairi and Houko bath themselves in pleasure with Ikuro, and getting to the know the goddess herself, the girls might start thinking this might be a blessing after all...