It seems that streamer-kun just finished the game on Citra. So to experience every part of USUM in Citra, we need to do this:

>Start Ultra Moon in Citra
>Play until the end of Grand Trial 1
(Photoclub crash on Citra, bypass using a post-photoclub save uploaded by kind anons, there are male and females one)
>Modify your trainer details in the downloaded save file and transport your Pokemon across in in pkhex, being careful to back it up and being careful to disable the pokedex updating (unless you are willing to wait for a more stable pkhex) https://teamcity.projectpokemon.org/repository/download/PKHeX_BuildWindows/15452:id/PKHeX%20Build%204013.zip
>Play until the Elite 4
>Like in SM, the champion will crash if you face him with more than three pokemon, use only three pokemon and there is no crash
>Beat Giovanni