Guinea Pig wa Ori no Soto no Yume wo Minai

Taking place in the future, research on male pregnancy is underway to halt the decline in population. Nagisa Fuyumi, who had been forced to become a test subject even though he did not wish to become pregnant, has lived in the institute for five years without ever becoming pregnant. While living in his new, lousy life, he meets his childhood friend, Hayato Hinozaki, who he once admired and fell in love with, but now they're meeting each other as a test subject and a researcher...?

(Source: J-Publishing, translated)