Fire Emblem fans when they won’t play the games instead of learning about them via horny reddit memes.
Anyway I can’t believe this thread isn’t locked yet but if it’s gonna stay up anyway, then: the actual reason this is a bad idea is because FE romhacks are just a weird space to explore topics like this. You’ve got the silly looking map sprites and the kinda cartoonish combat animations and the cute mini portraits and all these bright colours. It’s the same reason why a lot of the edgier pokemon romhacks get joked about all the time, they’re just kind of absurd in context.
Exploring themes like sexual taboo is not a moral failing and can be done within the realm of fiction for sure, but it’s an awkward fit for a GBA romhack. Moreover, the reasons you give for why you’re interested in exploring it are, bluntly, bad reasons, and don’t justify making such a leap. Its inclusion would, very likely, make your script worse. There are just several substantially better ways to do the emotional beats you want to do.
The vast majority of the people in this thread taking the admirable pro-incest stance are doing so with a really weird “yes, king, don’t let them cancel you!” vibe. Guys, Game of Thrones was an absolute cultural cornerstone for like a decade. People thought that one Lannister guy was like peak fiction, and he was so incestbrained he tried to kill a child over it.
Nobody relevant is actually going to crucify you for writing stories where these things happen; the actual issue is that most people on this forum are not George R R Martin. If you can’t see the reasons why you should try not to include touchy and taboo topics in your gameboy nintendo game romhack, then I’d wager you’re probably not quite ready to handle those topics in a more suitable medium, either.
That’s not meant to be a dig, mind you - when I was an aspiring writer, I also had a moment where I decided I wanted to tackle some weirder, more serious themes in my writing, and I quickly found out that senseless inclusion of these topics is almost always a bad thing. See, for example, how by the end of the thread you’d decided to omit the plot point - the goals you’d stated were simply better served with a lighter touch. Unless you have very good reason to, it’s very rarely correct to apply a freight train of a topic to your script.
Also some quick shout outs
yes you do lmfao, going “you should do the incest thing” by pointing at examples of games where they have really terrible incest inclusions that make their scripts demonstrably worse, or are written so terribly that incest is accidentally implied, is not the silver bullet you seem to think it is.
JasonGodwin7 jumpscare 
again, this absolutely does happen. There have been multiple hacks with these kinds of “dancer sold into sexual slavery” type characters in them that have raised some serious eyebrows, usually because it’s an extremely heavy topic to include and is frequently done so way too nonchalantly. Obviously, these topics can be, and have been, tackled competently and tactfully; that doesn’t mean they’re worth wading into unless you seriously know what you’re doing.
it’s not, but this is a very intentionally obtuse way of approaching this and you know it. Nobody is going to a romhack for a lesson in morality, and the general fearmongering of “people these days will hate you if you include a bad guy bc on twitter I saw the dumbest people ever getting into an argument on the website where the dumbest people ever go to argue!” is turbo-overblown, but like… Your writing doesn’t exist in a vacuum. If you write something morally reprehensible, but do so in a way that makes it seem like you really don’t think that is the case, you are as within your rights to write that as your readers are to think you’re a slimeball for doing so, and so it’s pretty fair to advise that you handle those kinds of topics with an extra degree of tact.
Like, framing this shit as a “be true to yourself” thing is stupid, bc anyone who’s ever done serious writing knows that including every random whim that comes to mind will make for a terrible story, and a big part of the writing process is rigorously testing your ideas to make sure they’re sound. A writer isn’t compromising the purity of their artistic vision if they decide the incest plotline will be distracting to most viewers, they’re just writing a better story.
yes it would lol, people still find that shit weird as fuck with or without offspring. Please, FE gamers, draw less of your worldview from porn. I already commented on how fucking weird the other part of this comment is.
ok I don’t have anything to reply to with perma he’s just based and correct, love you perma 
but also his work is a good example of what I mean, but in reverse; Deity Device deals with some pretty heavy themes of spousal abuse and the like, which could easily come across as tacky or over the top, but is instead monstrously effective at establishing the villains and leads to a lot of really chilling scenes. Permafrost is also, probably, somewhere in the top 3 writers on this whole site. I would not trust most other writers, including some I already like, to tackle those same themes even half as deftly.
Basically;
is still true. Don’t fuck your sister, folks.