Falsic

It's called sarcasm.

If reasonable constructive criticism is all it takes to set someone off to where they're threatening to stop writing the story, why are you concerned? They're just looking for an excuse to stop. They could easily ignore what they don't want to see, especially when no one's throwing insults or jeers. If the author isn't happy writing (which they're clearly not), you shouldn't let them hold you emotionally hostage. Let them pursue whatever passion relaxes them on their busy schedule.

The writing is more feminine than you'd normally see with these types of works, so you may be wrong here. This doesn't come across as a dude trying to write Yuri. Doesn't mean it isn't or that there is anything wrong regardless; it's just not as offensively obvious as you make it sound.

To reinforce this point, the author has issued the 2nd (last) warning after receiving constructive criticism. They will stop writing if they get any more, so it is not an exaggeration to say it's take it or leave it.

I'm a little confused on this statement. You're asking for honest improvement items here, but when we comment inside the work with constructive criticism, you threatened to stop writing entirely out of fury. Your ask for honest feedback here may need to be revised. Otherwise, you may be creating a self-propelled situation for yourself.

I... think you should clarify what you define as nitpicking. People from different countries define it differently. What's the difference to you between healthy criticism and nitpicking capable of erasing your motivation. Excuse my candor, but are you not looking for any constructive criticism whatsoever? Authors see more than what ultimately turns up in the review pane, so maybe Im missing something, but from what I saw, there isn't anything particularly nitpicky.

It would be excessive to do it anytime soon. The author already spent several dedicated chapters to getting HoT powers. Plus, Acheron's powers aren't free. The author needs to consider whether she wants the MC to go through that level of baggage. For example, losing her sense of taste and the severe dulling of her emotions. It looks like the author's chose the herrscher of origin route... which is in the complete opposite direction. Mei's origin transformation completely lifts the pall she's had over her emotions, making her much more expressive and feminine. Acheron is... dull, quiet, and tired. These are two different extremes.

I think you're rushing things and not thinking events through. Ex.There was no spar after training for the village leadership to see where she was at, there was no real discussions with her teammates on the status quo over the last year, just mindless plot. You even have her demonstrating a sharp immaturity here by gawking excessively at an enemy nation. Immaturity's cool... when you're not trying to show the MC's growth and when you properly address peoples reactions to whatever you're presenting. Is she so untrained as a shinobi that she can't compartmentalize this nostalgia when on a diplomatic mission. You're at the enemy's gates for the strongest nation in the world... and you're starry-eyed? This is all well and good if you have a direction you're trying to go, but... by your authors notes you don't. My recommendation would be to think about how a shinobi in this era is expected to act, compare that to Ei, and see where you want her in that spectrum... and what the subsequent consequences are for her.

An interesting thing to think about is that Honkai Herrschers don't really need to learn. Bronya's cinematic is a good example. She goes from being a floating manechin to doing stunts that would make Simon Biles jealous. That's not mentioning their immediate command over their powers.

I think you may be rushing the power scaling a bit. Ei can't even go on a mission without passing out, and you're teaching her sage mode...? Sage mode training would put her at sanin level... assuming she didn't finish. Perfect Sage mode, something that took the 'untalented' by Kishimoto's intent Naruto to Kage levels, would put her at her father's level. By feats, the third Raikage is the strongest kage after hashirama, and even if he was guided into doing so, Sage Mode Naruto was capable of killing him in combat. I hope you understand how OP Sage mode is. It's fine if that's what you're going for, but I'm just trying to make sure you know what you're setting up here.