I thought the whole problem was if she was unhappy with the world, she might replace it completely... a good mood would imply she is happy with the world, and should therefore be disinclined to replace it with something else...
I think Itsuki just doesn't want to be out a job.
Oh. I get it.
If she is utterly satisfied with the way the world is (from her perspective) she might stop wanting aliens, time travellers, sliders and ESPers around her anymore. Which could possible result in her replacing the world with something exactly like the way it is now, but without the weird.
Thus not only putting Itsuki out of a job, but removing his powers.
^^That'd make an excellent ending maybe, ending the show on a callback to Shohitsu. Or, alternatively, just showing how happy Haruh does not mean no complications to await either.
