The residents of the Underground Federation never refer to its full name.
"The Twin Goddesses' Republic Federation," this title, with the two goddesses not frequently residing in their homeland, is almost completely unacknowledged by the populace.
They indeed are very grateful to the two goddesses for granting them the ability to live underground.
However, gratitude does not equate to reverence.
For the underground residents revere nothing.
They do not revere monarchs, parents, or gods.
They even lack the concept of state, territory, or ethnicity... because their "territory" is constantly being expanded, and they were originally an assembly of many "failures," even now their numbers continue to grow.
In contrast to the narrow world above, the Underworld with its near-infinite space and extraordinarily abundant resources allows the citizens of the Underground Federation a considerable degree of freedom.