
that makes Yona the rightful heir in the throne. Soowon would be the King if only his dad died but the moment King Il ascend the throne, he lose his chance on becoming King (unless he kills King Il which he did and Yona who is the heir)... meaning the claim that the throne is his is not true because his father didnt even become the King... I just hate those tribes and the advisor for saying that the throne is for Soowon...

' I just hate those tribes and the advisor for saying that the throne is for Soowon.'
they wanted to bring Kouka kingdom back to the time before King Il ascended to the throne, they wanted the kingdom to be the same as when Soo-Won's dad was meant to be the heir, because Yu-Hon was the 1st born heir, and Il was just a spare if Yu-Hon died.
saw a random video on youtube that in ancient and medieval times that in a royal family it's the first born male who becomes the heir the throne, the 2nd male born will get involved in clergy. I guess at that time it was never heard of a 1st born female in a royal family to became an heir to the throne, so either way Yona was screwed of becoming an heir.
King Il married Kashi the priestess apprentice, a friend of Ik-Soo, who was also a priest apprentice, now I get why after Ik-Soo's introduction (in the early manga chapters) he wasn't a royal priest anymore and ran away into hiding. and I'm speculating that after Yona was born, king (at the time) Yu-Hon found out Kashi was a priestess apprentice, knew of queen Yon-Hi's secret, she was killed, king Ill killed his brother. years later to get even, Soo-Won killed his uncle and was about to kill his cousin Yona, but our strong (at the time general) Hak saved Yona.