It’s called condoms
Bro is never explicit when they put on a condom, implying that they didn't, besides that they fuck and don't change their position even after they come, so how the fuck will a condom endure
Eh tbh it must be manhwa logic The logics that never made any sense
The only reason for Doyun not getting pregnant is really bc he's recessive and his body isn't that fertile, bc they actually hardly use condoms...
Baby baby bab baby baby I NEED A BABY FUCK THEY HAVE SEX ALL THE TIME HOW THE FUCK HE IS NOT PREGNANT OH MY GOSH