I think the 'dreams' were more like different time loop that come after each other, and who/whatever can see these loops made small adjustments after each end of the world to try and fix it.
In the first, most raw timeline, Makoto basically was alone, went insane and all "Hey you know microwave? You know what happen if you put egg inside it?"
That established that he can't be left alone so...
In the 2nd time line, Tomoki, Mr. Shut-in, 'somehow' find and rescue Makoto at the border. He became 'guided' by Lily's wish for ruin on the world that took her mother away, and follow it even after her death (which honestly put me in the mood to read some 'insane villainess and her loyal servant who follows her against the world' sort of story for a while )
Aka the one that turn a country to dust.
So now they know how he kinda imprint the first wish of hte person he trust and then follow that to terrifying degree so....
3rd time line, Tomoe and Mio were there (and have romantic relation with him), and Makoto decided to join the demons to fight Bug, but that result in the death of those two.
In this one, we get Tomoe herself telling Makoto that maybe he needs a 3rd attendant to balance out the two reckless hotheads Tomoe and Mio, and probably a guy since that way they'll be more accepting of the new kid instead of seeing them as a rival.
And now we have Shiki.