Moon is definitely from bully is my lover, moon in harem hotel looks completely different, & is a minor character.
I spotted Annie from Eternum immediately in the mall though haha.
Ripples has the MC play house in the rift, and a cameo from Stabby from Once in a lifetime
MBIML/Sicae also reference Eternum a lot, and a cameo from Alex
Lot of cool overlap in the top series