Slipping into first-person narrative is always a challenge when the RP traditionally uses third-person. It can certainly suit some stories, however. This one seems unclear on what it wants to be. One important thing to consider when writing in the first-person is audience: who is the narrator speaking to? That informs what you'll be telling the audience, and what you'll be leaving out. It tells you what tone you should be keeping.
At the very end, you include the line, "I shall continue my tale again soon. I wish to give those who read this some time to digest it." Rather than clarify, this confuses the question of audience. Is this breaking the fourth wall, or is Lurius writing something down for others? If he's writing something for others to find, to what purpose? Just to let people know what the Outside Ones are? If so, he doesn't do that. Is it to tell them how to fight the Outside ones? He doesn't do that, either. The frame of this story is third-person limited -- it's not the narrator telling us his story, it's a story being told about the narrator.
First-person writing is allowed, and expected, to omit details because you're writing only from the narrator's perspective. It's more focused, sometimes more emotional, and yet less reliable. I would propose rewriting this, in fact. Put yourself in Lurius' metaphorical shoes and decide the following: when is this being written, where is he while he's writing it, what is he trying to pass on… and how will it be passed on? Will it be sent in a letter to someone, stuffed in another book to be found, left behind in his home for others to find? "My name is Lurius. I am one of the demvir, but burdened with knowledge that no one else seems to have, not even others of my kind. While I can, I must tell you about a grave threat: the Outside Ones. It may sound like the rambling of a mad man or like my cranium has been damaged, but read on. You must."