Can anyone point me to guidance on Breeding, I cannot find 'Ciguapa' anywhere.
There is no 'Ciguapa' in Strive, so you cannot catch or breed them.
Therefore you are probably using the AricsExpansion mod, which has a hybrid race called 'Ciguapa' if you have Ralph's Tweaks enabled before conception of the baby. There aren't any guides for breeding that I know of, so I just point people to the expansionsetup.gd file that has the code for the hybrids. The requirements for your goal is a child that is least 50% Nereid, they have to female, and they need a nature affinity of at least 70. Given that Nereid have a nature affinity of 50, you probably need to have the rest of the genealogy be made up of a race with a very high nature affinity like Dryad or Goblin.