Premieres July 2025. Check out the ANN article for additional information. Synopsis for the source novels from AniList:
Naofumi Iwatani, an uncharismatic Otaku who spends his days on games and manga, suddenly finds himself summoned to a parallel universe! He discovers he is one of four heroes equipped with legendary weapons and tasked with saving the world from its prophesied destruction. As the Shield Hero, the weakest of the heroes, all is not as it seems. Naofumi is soon alone, penniless, and betrayed. With no one to turn to, and nowhere to run, he is left with only his shield. Now, Naofumi must rise to become the legendary Shield Hero and save the world!
No idea. Only the demihuman characters work this way. Nobody gets old old from leveling either. I would understand it better if it were just physical progression, but the added insult of the slave character in question getting passed around from slaver to slaver while being stuck with the mentality of a child is just straight up fucking bonkers. IIRC she even loses the slave crest that binds her to the MC but she insists she undergo the process of being enslaved to him again because it "strengthens their bond" (LOL.)
Yeah, that was what I was referring to when I said the girls want to be enslaved. I think I heard that she also convinces another girl to be enslaved to the MC to make her a better fighter or something.