Guardia Succession (Order of)
How does the royal line of the Kingdom of Guardia operate? Does it work through male or female heirs? The facts:
Marle is descended from Aliza, who is descended from Leene.
King Guardia XXXIII is spoken of as the 33rd descendant of the throne.
The Kings seem to rule with the most authority.
Under this idea, the son or daughter of King Guardia XXI and Queen Leene would have eventually produced Queen Aliza, who would have had to marry back into the family (barring outright incest). This is fine, as twelve generations would have separated their genetics. This idea is supported by the fact that King Guardia XXI is definitely large and in charge during 600 A.D. The royal family may also be extensive enough to allow varied descendants of Leene to exist.
Usually, males marry into the family. An exception was made when Queen Leene married King Guardia XXI, as a female heir may not have been available. The line proceeded with males marrying in all the way to Marle, who married Crono (and by extension he became a regent). This system is evidenced elsewhere in the game. When King Zeal dies, Janus does not by default become King; rather, Queen Zeal remains in her position. (Note that this is mainly a coincidence.) Sexism is also seemingly absent, as even Ayla was able to be chief in prehistory due to her strength and merit. The Kingdom may be matrilineal but patriarchal. This possibility is wounded slightly by the fact that King Guardia XXXIII is referenced as the 33rd descendant of the throne; this simply may be a turn of phrase, however.
From: Theory (Plot and Other)