"Right. I don't want Flowey to come back, and you don't want Nyx to return. So I have a plan."

Whether or not Ryoji likes this plan is irrelevant. Of course, if he agreed to let Asriel take his soul, it would make his job much easier. But nobody in their right mind wanted to live without a soul; not even Chara loathed themself enough for that. If he's the reincarnation of Nyx, this will be a difficult fight.

"I'm doing everything I can to take over this island. Once I'm in control of the timelines, I'll get to decide who leaves and who stays. Nyx will be permanently banished, and you'll be free to have a normal life here until you pass of old age. It's the way it should be and I'll make it so."