Writing Quality: Average
The grammar is generally good overall with barely any quirks in syntax. My pet peeve is the usage of colons for dialogue like,
Kais: "Hi."
Sona: "Hello."
Using this form, and even the overall style of prose you're writing in reads very much like a theater play than an actual book story. This detracts from the immersion, making it feel like a narrator is continuously talking to me rather than me, a reader, getting immersed into the story. Additionally, it automatically limits and deprives you of speech verbs like he chuckled, screamed, wept, groused, etc. These give a lot of character and immersion to your story, so by using colons to express dialogue, you're missing out on further crafting a world and cast of characters that's easily visualized and experienced by the reader.
I also noticed that the dialogue itself needs a lot to be worked on. Much of certain sections feel very unnecessary where by the end of the whole conversation, I feel like I got nothing out of it. For instance, the conversations about killing the dragon between Sona and Kais was just a bunch of back and forth that didn't lead anywhere. I would suggest just cutting this out or omitting parts of the dialogue entirely. This also includes skipping the beginning first scene and jumping straight to Kais being attacked at home by two half-psychics. I believe this scene to be engaging and a better story starter.
Additionally, the switching of first and third person, especially in the first chapter, along with the switching of perspectives and settings from Kais to say Ro, is very discombobulating. It's confusing and clunky. If every chapter was designated to one perspective, then I think this issue would be cleared up somewhat. But currently, with the cutting from one perspective to the other as well as the shifts of "I" used in first person of Kais to then speaking about Kais and comparing his and others' powers doesn't feel very fluid or harmonious. I suggest sticking with one narrative and one perspective, at least, for every chapter. Lastly, as general, short recommendation, increase range of vocabulary.
Update Stability: Great
Nice and steady, several releases every week, good job pacing yourself!
Story Development: Under Average
The main problem here is due to the unnecessary dialogue which makes it feel like it's a bunch of back and forth and not much moving ahead. The only part where it felt like a good pace with necessary and interesting dialogue was when Kais was attacked in the first chapter by two people in his home. I suggest applying this to the read of the dialogues in the later chapters. I touch on this later in the world background below, but the story had a lot of telling rather than showing. I want to be able to envision Kais as he's on the island and moving around and interacting.
Character Design: Under Average
I don't have much of a grasp on the individuality of the characters. I get a general sense, but most of that is largely derived from their dialogue, which isn't enough and should be supplemented by more character introspection and details on their gestures and mannerisms. You do some of this already, but it needs to be pumped up more. With Kais especially, since he's usually in first person, I want to see more of his feelings rather a "monotone" reaction of the events happening around him. When he says that two half-psychics can't compare to a full psychic like him, I want to feel more of his confidence, show it, don't just say it. Overall, I'd like the characters to be more differentiated and definable. Some of the issue lays in having too many characters that the story is following, so we don't get a clear grasp on each before moving onto someone new.
World Background: Average
This actually is in-limbo between under-average, but since I deemed it to be on the stronger end, and one of the better aspects of your story that you did well, I bumped it to average. I understood what the world was like and where Kais was generally; although, the switching of narratives and perspectives definitely did trip me up. The main aspect that needs to be worked on is to do more showing and less telling of his settings, world, and what he's going to do. Again, this goes back to the beginning point about how this story reads more like a theater play script than an actual book story.
In conclusion, you have a good starting set of tools to make a good story with your writing abilities, but the organization and scope of the story is lacking. These are all fixable without impairing or greatly changing your essential plot and story, however. So continue writing, keep learning, and good luck!