Oh for the king thing "The first king of Valla who had a deep friendship with Anakos" could just mean none of the previous Kings were close to anakos at least that's how I took it…
Nah, the phrasing of the Japanese line makes it clear that the founding king, Ryuurei, was very close to Hydra. Subsequent generations were also close; close enough for Hydra to teach them his song to calm him. Hydra began to drift away from the public as his madness began to take root. The final king still had faith in him even as public opinion turned hostile, but Hydra turned on him before he could even try using the song.
My personal theory is that the initial settlers of Touma were Hydra’s closest worshipers. He took them to a secret pocket dimension he created when the dragon war began to heat up because he wanted to keep them safe. Look at how temple-like the palace of Loulan is, for example.