
It doesn't matter if someone later "changes their mind".
It's rape.

I pretty sure it is rape.
Bum is not in the right state of mind to give consent. If we look deeper, he's held captive, had mind games played on him to make him want to be captured and to be scared of leaving, and to depend on Sangwoo completely. Hell, Sangwoo, captured a girl, and then used weak minded Bum, to lose it and kill another person. So I'm pretty sure it's rape.

Also, not hating the story, I like it xD
I can't tell if Bum was raped or not. At the beginning he kept on saying No but then halfway through he got along with flow with Sangwoo, but then when he saw it was the dildo he kept on saying no again ( ̄へ ̄) ╮( ̄▽ ̄)╭