Nobody seems to have a clear answer on who exactly is 'key' in 'Dark Realms' because honestly, the novel just throws characters at you like confetti. I stuck with it for about thirty chapters, and every other chapter introduced someone new with a convoluted backstory, only for them to vanish for fifty pages.
You've got the main guy, Kael, I think? He's supposed to be this chosen one with a shadow-wielding power, but his personality is basically 'brooding' on a loop. Then there's Lyra, the scholar, who exists mostly to explain the lore in info-dumps. The most interesting one was this side character, a grumpy alchemist named Verrick who showed up for maybe three scenes, stole every one of them, and then got written out on some fetch quest. I gave up trying to track who mattered. The real key character might be the author's notes, because you need them to understand what's happening.