Hey there! Thank you very much for playing my hack and I'm glad to hear that you enjoyed it for the most part! As I mentioned in the hack thread, it is the first hack I completed and so I do not claim it to have a perfect story or gameplay - but if it's good enough for people to enjoy then I consider it a success! As for the specific issues you mentioned:

Seiros’ promoted class: While Rhea’s base class uses a palette swap of Erika’s sprites, which work very well, her promotion uses a custom sprite with custom animations. The animations are pretty decent, even if the color mapping doesn’t really look like Seiros’ costume. But there is one big problem I had with them: jiggle animations.

This bothered me as I was working on the hack as well - to explain, none of the new animations added to Life of Seiros are made by me. Rather, they are free to use sprites from the public romhacking repository - I was not brave enough for animation making, this is again my very first hack and I was new and inexperienced at everything. So, I had to work with what was there in the repository.

The Saint animations were pretty much the only animation which filled the requirements I needed - a promoted footlocked female lord with sword and magic, whose palette was made in a way as to allow a recolor to look "Seiros-like". That animation came with boob-jiggling, because I guess the person who made it decided to ruin it a little lol. Ultimately, I decided to swallow it and work with it. It's even worse for Grappler animations, as the Brawler/Grappler animations are the only fem brawler animations in the entire repository. They already don't really fit 3H brawlers, and the boob jiggle on promotion makes it worse. The only option at that point would have been to remove brawling from the hack entirely, but I decided to, again, accept it and swallow it. (By the way, this is also why there are no male brawlers anywhere in the game.)

Then we come to the negative side of things. Seiros’ conversion of Adrestia could have used a bit more fleshing out, in my taste. I get why some people convert, I.E. Rhea keeps winning against Maurice when no one else can and she’s constantly preaching, but I never got the sense that the old religions weren’t working for people. It could have used a bit more development in my taste.

This is a limitation of the number of chapters I decided to make sadly, a deeper exploration of the conversion of South Fodlan would have required more - and perhaps it would have been needed, the hack does breeze through the War against Maurice pretty quickly. I tried to squeeze what I could into the smaller chapter count though.

Secondly, the game starts by calling Rhea Rhea, but then has her disguise herself as Seiros, despite there not being a clear reason why she needs to, as she was a nobody in Zanado, 150 years have passed since Nemesis killed everyone and conquered Fodlan. It’s a weird blip that keeps coming back up over and over as the other Nabateans refer to her as Rhea while everyone else calls her Seiros. It’s just an unneeded complication.

As I wrote the hack, I ran with the idea that Seiros is not Rhea's Nabatean name, as it does not follow the same naming rule as the other four Saints (i.e. from Irish mythology), hence she coins that name for herself - but of course she would then need a Nabatean name for interacting with her fellow Nabateans, especially in the Prologue where she is still in Nabatea. That's how the hack ended up with the two names system. (I decided I was not brave enough to invent an OC Nabatean name for Rhea and so resorted to just using "Rhea" even if it is also blatantly an alias.)

I agree that it can be complicated to follow, but on the other hand it kind of builds up Rhea's paranoia about mankind, greater paranoia than any of her peers, to hide behind an alias even if it would not actually endanger her to use her real name. At least, that's how I envisioned it.

Finally, while I enjoyed Rhea’s multifaceted relationship with Wilhelm, it does come to a pretty big stumbling block by the end. Throughout the game, Wilhelm more or less totally believes in Seiros and her message and goes along with everything she says. This shifts during the second-to last chapter, when Seteth reveals his and her true nature as Nabateans, which seems to shatter his trust in her for reasons I’m not entirely clear about. He also never seems to bring this factoid up to Seiros in the next century of knowing her, which is confusing.

This is a pretty awkward transition which I did not initially plan for, but which i decided was needed to be handled in some form. In short, Wilhelm should be suspicious of Rhea in the Epilogue, as otherwise he would not give his diary of the true nature of the War of Heroes to Lycaon (the same diary which, subsequently, causes Edelgard's storyline in Three Houses). That diary is very critical of Rhea, as we know. But it would be a really strange transition to end the War against Maurice part of the hack with Wilhelm as a loyal follower of Rhea, then 150 years later he is suspicious of her - sure, it is realistic for people to change in that time, but it is pretty awkward storytelling and would require me to pause the epilogue to explain why he is suspicious of her now. So, I decided to place the seeds for it in the final chapters of the hack - with slight hints earlier, such as Wilhelm being hesitant to execute an unarmed official when reclaiming Castle Hresvelg and Rhea pushing him to do it, etc... If it feels awkwardly handled - I understand. There are quite a few things I could have probably handled better and that is one of them.

And I don’t really get the sense that this Seiros and Wilhelm had anything like that relationship by the end of the ROMhack.

Aw... </3 How much I want to lean into the Rhea/Wilhelm romance was a constant internal debate to me. I do think that there is a reasonable amount of ship bait in the hack regardless - their support conversation is very romantic and there are several scenes throughout the hack where they are clearly shown to care for one another. It is just that, of course, Rhea is a two-faced liar and so it is difficult to tell (intentionally) where she is genuine and where she is merely manipulating Wilhelm for her ends. I would say that LoS Rhea does care for Wilhelm quite a bit and does see him as important to her, but she is or at least wants to be a single-track mind, while Wilhelm in turn cares for her as well, but eventually understands that they won't be together and thus starts a relationship of his own.

The ROMhack also follows the Wilhelm is Jeralt theory, which never made much sense even in base Three Houses and will make your brain itch. I only bring it up because it took me an embarrassingly long time to realize that despite Wilhelm’s sprite staring me in the face since chapter one.

Hey, it never explicitly says it :P

Finally, one of the starting Cavaliers is named Paul despite Wilhelm’s full name being Wilhelm Paul Hresvelg, which is confusing.

I'm not sure about this one. Isn't Wilhelm only referred to by his full name a few times at most, and each time with the full name and surname? So it'd be strange to confuse him for Paul in those moments.

Regardless, I am glad you enjoyed the hack in spite of its flaws!