The Shalarin originally come from the Sea of Corynactis on the far side of Toril. That is true now, but what if it had not always been so.

In an alternate version what if the Sea of Corynactis was one of the areas of ocean surrounding the continent of Laerakond before the Tearfall.

What if the Sea of Corynactis was taken to Abeir along with Laerakond when the worlds were separated.

Thus the Shalarin are from a different world and at the same time hail from the Sea of Corynactis which returns to Abeir-Toril in -339 DR along with the rest of Laerakond.

The Shalarin exist in a rigid caste structure that exists from the moment they are conceived. This structure is so inherent to their nature that they even apply their behaviours to non-Shalarin. The origin of this caste system lies in the Shalarin's distant past when they were a servitor race to the batrachi before they ventured onto land. The batrachi modified the Shalarin to be naturally subservient and obedient, something that persists to the present day.

They were abducted to Toril by the Wildtide Gate which was constructed by Dagon who had a personal vendetta against the gods of the Shalarin who were also the gods of the batrachi and who foiled Dagon's plans to dominate that ancient creator race.