After reading 21 chapters and skimmed over the latest for reference, this is what I'd have to say.
Note: I am using he/him pronouns for the protagonist since the sex change was forced on him, assuming that he did not readjust his gender to his changed sex (As this may be lost in MTL: sexual identification "I am a man" vs body "I have boobs and a vagina").
World
As far as military and fantasy are concerned, I'd say you're fine for a general audience. For someone like me, who has little experience in either beyond what other authors made of the topics, nothing feels glaringly out of place.
The "that time in x" name dropping is out of hand, though, so if you're looking for a way to improve the earlier chapters, that'd be a decent place to start.
You yourself stated that it was confusing to readers and I am inclined to agree. It doesn't influence the immediate action much, as that is relatively grounded in the early chapters, but the entire battle against the dragons and Atlantis part of his backstory doesn't really fit in until now, despite you mentioning it enough to make it seem important. The glossary does explain a lot, but it can be a bit stuffy when looking for crucial information.
How old would the protagonist need to be to have participated in events that there is no remaining public knowledge of and one of the central locations (Atlantis) is a long forgotten ruin at present?
Characters
Caesar/Elise for the most part matches the veteran he is supposed to be, but certain decisions seem plot-driven, like not trying to get rid of the collar at all or thoughtlessly signing a contract from someone who already fucked him over once without reading it.
His laid-back attitude regarding his sex change and family of not actively looking for a way to them can also seem off at times. He just wordlessly accepts a lot of things and focuses on what's around him (his new wife) over either.
Tamamo-no-mae initially came across as a bit of a rushed romance character, but their interaction after the marriage drastically reduced the issues I had with her. What the future will hold for her I cannot know without reading your book, but at least for now she's definitely more relevant than the "tutorial reward lover" I took her as in the beginning.
But as things stand right now, her stoic nature is even worse than the MC's and with no goals of her own to pursue, I fear that she will become like the celestial body she represents: a satellite of the MC with no involvement in any external matters.
Which, for me, would make her a bit boring tbh. But she's your character, so take this as you will.
Plot
You say the plot starts in the middle, but I found that things actually took their sweet time to get going (some still are).
After a bit of setup in the first chapter, you have combat scenes back to back. They are not out of place and well done individually, but there's a few too many of them for how little plot impact they have.
Afterwards you change it to a sort of supernatural anime setting. No war, a gambling father who leaves him comically without funds, enslaved women being thrown at him...
Solely looking at the first 21 chapters, I think the biggest potential issue wouldn't be whether you handle the individual topics well but that that the story jumps between extremes of using them.
Just keep track regarding how much of a certain thing you've done recently (war, uncovering his past, his family or romance) and try to keep them in the balance you want them to have unless something really important happens.
Writing and Grammar
You didn't want me to spend my time on this, so I'll try to keep it short.
As far as pronouns go, you drastically improved through feedback, but the early chapters deserve a polish in that regard in my opinion for reader retention.
Huge block paragraphs do stay, though. You broke the dialogue down to fit a visual novel style, but where would those walls of text go? Break them down. Your grammar is relatively readable, but this is the biggest issue with it. Sentences being a bit chaotic gets a lot worse if you put them into one homogeneous block.
So that'd be it. Hope I was able to help in some way.
Thank you very much for your analysis. Because it has helped me to see how others can see the story, and from the point of view of someone who reads it for the first time.
The World:
Well, it's understandable that everyone thinks the same. I think my biggest problem is that I did not want to bombard readers with too much information, so I reduced it to the minimum that I could to understand what was happening immediately but that pointing out that previous events are really important and that what happened at the beginning is a consequence of them. Most of the heavy stuff is explained later in the novel, little by little. For example, a summary of the war in Atlantis is mentioned in chapter 69,
The only thing I was looking for was to save things for later in the story and not drop all the ammunition in the first chapters.So I was not sure if that is playing against me
Regarding the age of the protagonist, well it is difficult to explain that way without the context. In theory, he should be like 20 or 24 years old. But the war against the dragons lasted 10 years, in which when it ended it was returned in time to the day it started, so mentally it should be about 30 years old. In fact, I was thinking of talking about that in a specific chapter, but in one of calm or comedy, The characters debating their real age and realizing that his story does not match their age.
As for the glossary, well, it is written according to the current state of the novel as well, because if I start to write certain details that I am deliberately saving, they could kill the surprise of what I have saved. Things like how the stone of wishes works and why the protagonist does not want to use it. What was the price to pay, what happened to Nanami? These are things that I'm saving for the right time.
Atlantis is scheduled to appear multiple times in the novel, and with each appearance always bringing bad news, like Dracula's castle in Castlevania.
The Characters
Caesar/Elise:
Well, I wanted his personality to be that of someone who has already seen so much nonsense in his life that he is already don't giving a fuck, he is only interested in being with his family in peace. As for his attitude to what happened, well, it is also explained later as always, but the idea is that this was not his first time. During the war against the dragons, he was forced to pretend to be Nanami and lead Atlantis. He himself indicates to his family, his mother, and sister, that he wants to continue as if nothing had changed and they treat him as he was original. That is why he is not actually surprised as he should. At least that's the idea, once again I don't know if that is playing against the enjoyment of the novel.
Tamamo-no-mae:
Well, the idea with this character is to be a support for the protagonist, she is mainly to help the protagonist emotionally when he runs into an emotional wall. Those moments when he really encounters something that he fears. But I didn't want her to feel like just a brainless character who only does what the plot needs. I thought that with the background of the real legend, it would be interesting to see her and the protagonist act as a team. See them having good or bad times together like despite how she behaves, the protagonist tries his best to get along with her.
A story arc has been planned for her as well, but it won't be seen until much later when it is assumed that she and the protagonist are inseparable. Perhaps to make the emperor who betrayed her appear again, bringing an internal conflict for her, about her feelings. She also thought that something tragic would happen and she would become the main enemy in a story arc near the end.But yes, I plan that she and the protagonist end up together, no matter what.
Plot:
This point is quite curious, because although the main point of the series is undoubtedly the action. And I thought I made it quite clear. In a poll I did recently, in Chapter 77, readers have told me that what they want to see the most are the slice of life and romance aspect. And I tried to keep them balanced, although I am not going to give up the action and military aspects. I am also aware that there are times when things have to relax and enjoy life. I have a lot of funny and funny stories in store for those moments.
The story is basically divided into worlds, each one with its theme and problems. So I thought that in order not to confuse more than it already is I make them only focus on the current objective of the problem in which the characters are involved at the given moment. If something from the past is wrapped up in current events then they will mention it. But those are recurring themes that are seen in-depth as the story progresses. Later they will return to them and see things that were left unfinished in the first trip
For example the world of angels and the father of the protagonist. The first works with money to buy products that they import from the Earth and that they use as exotic objects of collection. And the father the protagonist uses these objects to take advantage of what is happening secretly to help his family. His gambling addiction problem is just an afterthought to hide why he knows so many people in the right places.
Writing and Grammar:
Here is the truth I can not debate anything. I've tried my best but there's always something that eludes me. I thought about getting an editor to fix the first chapters, but at the moment I don't have money for that.
I put the dialogues divided into paragraphs by character, it is easier to realize when a new person is now speaking due to space. Well, there will be times when a large number of characters will talk about something and it will be chaos to keep track of the speaking turns.
Once again, thank you very much for your time reading and writing down which things caught your attention. I really appreciate your help and it has helped me to see how a reader without the knowledge of the whole background of the whole story can see it. I'll see how I can fix the start a little more and make it easier to understand.