@SuperOniichan
Page 5
Dude: Honestly, if I told Kyousuke and the others about it, they would want to leave right away... So, do you want to make babies?
Basically, his entire dialogue on that page is him revealing to Chitose that the only reason he didn't have his gang leave the MC's gang behind on dry land right away, was only so that he could have a chance at fucking Chitose in an attempt of impregnating her.
He sent the others on a deadly mission for a battery he knew they did not need, all so that he could have a chance of being alone with Chitose to complete his mission of having sex with her. His wanting to have sex with Chitose is, in other words, quite literally the only reason why the MC's group still believes they have a remote chance of being allowed onto the boat with this dude's group to get to safety.
Chitose knows that if she refuses to have sex with him, then the dude will leave them all stranded on that island, alone to fend for themselves against all these mutated and murderous insects, practically being a choice between A) Have sex with someone she doesn't want to. Or B) Sentence herself, and the others, to death by insects.
If this wasn't enough to make the case of it being a choice between Rape or Death, then to further back it up, look at Chapter 17.1 pg 11:
"If you do as I say, then I'll let you lot escape with us, okay?"
followed by "I never said that I'd be letting your friends board."
after the MC brings up the rest of her group who are waiting elsewhere.
And on Ch.17.1 Pg.16, MC opens up the paper Chitose gave her as she passed her by:
"It'll work out, Mutsumi... I won't let the boat leave before Kai and the others arrive..."
Chitose is only acting as a distraction, doing what needs to be done regardless of whether or not she wants to, so that she can hopefully make sure her friends can come back to the boat before it leaves.
Heck, his nickname is even "Never-missses Kaoru", because he is supposedly super fertile (or whatever it is called when a man's sperm has got an increased chance of impregnating a woman), and there's no telling how many women he's fucked have gotten pregnant in the past.