From COMIC X-EROS #72 (26/10/2018), high quality but censored version. Translated & edited by me.

Other available versions (low-res, lighter censorship):
JP: https://e-hentai.org/g/2178406/a587c3be2f/?p=3 , starting at p.147
CN: https://e-hentai.org/g/2359111/161c4954ac/

For the record, he reused the same characters 6 years later in https://e-hentai.org/g/3127327/e734a5d682/.

Is anyone else not seeing recent gallery uploads on their mobile devices???

Base +6, theboredotaku +7

And he mysteriously got bigger boobs.

Base +6, ginbrz +3, kamisking +6, Drevlik +6, I_Want_It +7

There is no way a man tits can get that big.

Base +6, theboredotaku -7, AdurnaNagra -6, Aegol -6

The artist is a little inconsistent about it, but from the chronologically first time we see him naked on page 6, it's clear that he had noticeable breasts and puffy nipples even before going through any special training, and they get even bigger in later scenes. It's a puzzling addition, since the doujin doesn't have a feminization theme or even mention his femininity. He's not even being made to take dubious drugs or anything; it's otherwise a mind break doujin with an infantilism subtheme.

Base +11, AdurnaNagra +6, I_Want_It +7, greatwave +6, facelessone +6, alllifeinfate +6, Slarka +11

Why does he have breasts?

Base +6, Slarka +10