#given that lucius “disappeared” at rakua i assume that if he had a child it would have been before that point

[amelikos]

The Terapagos flashbacks may have all been from Rystal's point of view since she is the one holding seemingly always holding Terapagos, and what we are witnessing are Terapagos's memories.

Also.. it seems like Lucius was only traveling with Rystal at first from what we've seen in HZ073. He only addressed her when he said "let's go", so maybe they both met Gibeon later on and he ended up joining them on their adventures. I wonder how they met him, and how the three of them eventually founded the Explorers (if we assume they are the original Explorers).

I assume that after whatever happened at Rakua, Terapagos used up all his power somehow for some reason and took on a dormant form (the pendant). Rystal would have taken the pendant and her and Lucius's belongings (the memoirs, and everything else) and kept them all this time, which is eventually how Diana would have found them at her place. (Going by the assumption that Lucius and Rystal were lovers and that they had a child together, etc. Diana apparently found someone's picture, which is shown in the preview for HZ074.. Terapagos seemed to recognize that person, so I assume that's Rystal. Maybe Diana has never seen Rystal before, so Rystal could be her grandmother? Which would make Lucius Diana's grandfather. We'll have to wait and see to know for sure.)