I did the mistake of rushing to read the entire manga, it makes things feels even worser, if you have a weak heart don't rush this, I felt gloomy for two days.
Is the mc not thinking about his body's situation back at home? He was already crippled after the first fall, I can't imagine what's became of him after the second one.
This is a nice plot hole, the girl got the collar mark just by insertion, the MC could simply penetrate many girls without cumming and still get the collar mark on them.
This is great, it's a nice slice of life, it's not about the mc storming the place and owning massive fortunes as usual when the MC introduces new technologies or new concepts.
Looks like they came up with a different ending of this situation, I think in the LN Akira was running around the big cannon thing with his bikeand shooting some of the plate until it came off.