I really like this story but I have some suggestions. Not that you have to follow them as I still will read happily 😁.
First, background on the main character. How does she come off, what type of posture, stance, and walk does she have, and what does her resting face look like? Does she show her true emotions on her face? Does she wear a mask of emotions? Does she have any specific mannerisms like crossing her arms or brushing he fingers through hair? These physical ques show something about the character and give more depth. The fact that she can kill without any remorse, that she seems to be dense to attraction from the opposite sex, or how her personality seems to change constantly should be explained and relevant. Also you should leave some room for development. Not that she has to start off as weak, indecisive, naive or anything of the like, but just that in some way her character will evolve as she interacts with the things around her whether that be in a positive, negative, or neutral. Does she have any interesting ir odd things about her character?
Secondly, there's not much info about the world she's currently in(first arc). I'm picturing Ancient China from context but it would be nice to have some more vivid descriptions of her surrounding. Is she in a realistic world? A mix of modern and ancient? A mystical world? how does she interact with her surroundings, even on an immediate level? Like how she feels about not having proper toilet paper or how her bed is hard. Or maybe because of her past she actually appreciates her current environment more. How does she go about the daily duties that she is most likely unused to? And how much does she really differ from the original host? She seems to be in nature up to chapter 6 as a part of the army, so how does she feel about the climate, terrain, plants, and animals around her? How does her past affect her view on war and violence? Does she have any survival medical or culinary, strategic knowledge? And if she does, why? All of these apply to life in the military in addition to fighting prowess. Then looking forward, what is her understanding of etiquette and interpersonal interaction in this world as she integrates back into society after war is over?
Thirdly, how does she feel when she interacts with the other characters in this world? Does she have a hard time connecting with them because of cultural differences and make little slip ups in her actions and words? Does she have some previous experiences or skills that allow her to assimilate more effortlessly?How does she modify her actions when one character in respect to another or does she not do that at all. Is she good with social interaction in general, or is she socially inept for some reason?
Next it would be nice to have a better understanding of the side characters. What do they look like, and what eccentricities or habits do they have? How does the mc view or percieve them and what are her feelings about each character? What are the other characters opinions of the mc and how do they change once she inhabits the body if they do at all?
Finally, how does she percieve her current situation and what is her main purpose or goal in all of this? What is the main motivator in her actions? How does being in a new body feel to her. She seems to be pretty calm about the whole situation so is there a reason for this? If not try to incorporate more relatable/realistic reactions to the idea of her having a system. An average person wouldn't be calm and collected after dying and being told all of these crazy things. Does she think she's dreaming? Does she go into shock? Does she ignore her feelings and act calm but then later on is affected by the realization of her predicament? Is she scared or even terrified? Or maybe she truly is calm and why would she feel one of these ways?
Anyway thanks for writing and reading my comment if you author. Take my words with a grain of salt👍😋