In all rape-related (criminal) cases, it is the prosecution who bears the burden of proving “lack of consent.” Because it’s up to the prosecution to prove (beyond a reasonable doubt) every element of a crime.
Normally, “lack of consent” is proven by showing that: the rapist used violence/intimidation (as a means) or the victim was already incapacitated (and the rapist was able to take advantage of that).
Here, the level of violence/intimidation is important. –> It must have rendered resistance “impossible or extremely difficult.”
This means: If the accuser could have reasonably resisted or ran away at any point, the court is unlikely to recognize rape. Having said “no” (alone) is insufficient. The court will also consider the circumstances under which the individuals entered and left the premises.
Below, a (Korean) Supreme Court decision from last year.
Thanks for reading!
I also recommend this post: https://klawguru.com/2016/04/22/the-serious-crime-of-false-accusation-in-korea/