"I hear his spells."
Translation:Zȳrha sētera rȳban.
Why is this Zyrha? This is difficult for me. I thought you had to be able to distinguish the classes. Setera is from the Aquatic class right? So why isn't it Jahon?
"Zȳ-" vs "Jā-" isn't about which noun it modifies. That's what the ending is for, and that needs to be for aquatic nouns. Whether you use "zȳhon" or "jāhon" depends on who "his" is in this case. Obviously, that's not clear here, so "jārha" ("jāhon" is a terrestrial form) should be accepted as well.
zȳhor vs. jāhor depends on the possessor's gender like English his vs. her vs. its, only that in High Valyrian this does not happen based on natural gender but rather the Lunar/Solar vs. Terrestrial/Aquatic.
It is the ending of the adjective that depends on the gender of the defined word like all others. So:
Zȳrha sētera rȳban. = I hear his/her/its spell. (the spells belong to a pre-defined lunar/solar noun eg. Daenerys or something like korze=sword or if it doesn't refer somewhere specifically, to an undefined animate being)
Jārha sētera rȳban. = I hear his/her/its spells. (the spells belong to a pre-defined terrestrial/aquatic noun eg. Aegon or something like blēnon=mountain or if it doesn't refer somewhere specifically, to an undefined inanimate thing)