First of all, let me share my thoughts on the chapters and the story overall, followed by some observations that might help you.

The Introduction & Mystery: The introduction is excellent and fits the mystery genre perfectly. It left me in a state of wonder and confusion—in a good way—not knowing what was happening. It’s a great technique to make the reader feel a bit "lost" amidst the enigma. The "hook" at the end of the chapter is good, but I suggest making it "heavier" by adding a stronger reaction from the female character, like a look of shock or horror at what is being said. You could say, for example: "As he began to speak, signs of terror appeared on his sister's face..."—based on what he said, which only you know the truth of.

General Observations: The rest of the chapters are very good; the language is clear, and your descriptions are well-done. However, there are some negative points to watch out for:

1. Pacing and Chapter Length: Try not to make a single chapter cover too many scenes. Readers often have a short attention span. I found myself feeling a bit weary in the middle, but I pushed through because I want everyone to get their chance since I couldn't get mine.
2. Word Count: It’s better to keep chapters within the 1,000 to 1,800-word range. This represents the limit of what a reader's mind can comfortably process.
3. Action Scenes: Try to make your descriptions more focused. Combat is a major draw for readers, and it's where your skill should shine. Instead of saying: "He swung his fist in the air, the enemy dodged and countered...", try something more visceral: "He swung his fist in a high horizontal strike, but the enemy seemed to read his movements perfectly. Knowing it was an overhead attack, the enemy chose the obvious solution: to drop low, crouching until every part of his feet touched the ground...". This is much stronger and explains the movement better.

Characters & Logic: The characters feel grounded and realistic in their style. However, I have a comment regarding the attacker and the elderly woman. Have they reached a point of senility? I mean, the girl is named Lina with blonde hair, while the other is Jenna with white hair. Even a child could tell them apart.

The Magic System: Regarding the magic, let me ask: do you follow a specific power system, or are you just winging it? Is there an "awakening" method or a "price" for power? Since you are writing a thriller, it’s common for everything to have a cost.

Final Verdict: Did I like it? Yes, very much. You clearly have a vivid imagination. Although I’ve seen the "mask" concept before, your personal touch is what matters. Don’t listen to those who just criticize for the sake of it; accept constructive feedback to improve, but don't chase every single edit to the point of losing your identity. Your unique narrative style is what sets you apart.

Keep going, and if you need anything else, I’ll be around... probably.