Imagine if he got resurrected at the location he died each time, and kept being teleported into the middle of the ocean each time he is forcefully isekai'd. Non-stop cycle of drowning and waking up more and more deteriorated irl
Or if he reappears at the location his otherworld body is when he's isekai'd, imagine if he got eaten there.
Nope, I don't buy it. I bet it's actually one of those gods or something that take the appearance of someone MC knows on order to keep their real selves hidden until the time comes.
Incorrect in just the previous arc Hanahana did not get one either.
https://mangadex.org/chapter/395932/11
I suspect it's the girls who fall in love with Youta before they mate with him don't get the collar and the ones he forces into it with his touch become his "slaves" hence the collar.
The other options for the collar are people who masturbate or give a blowjob and swallow before sex.