@TNT261 If a romcom becomes a harem, it would either be a harem early on or it would instead just be a bit harem like but we as readers know it means nothing (so it's fake; which I personally think is more insulting). And the battle transition is due to popularity of a single arc's battles.
Also, romance can often be added to anything. Super Hero movies don't get turned into romance flix, they just add romance. And that's usually to just improve the super hero part of it (aka, give personal stakes; often cause the parents are already dead).
Very rarely is there a weird twist where the type of story changes and if there is, it's often a gradual one that doesn't fully contradict the genre it already was.
MILF porn won't transform into gay porn, and gay porn won't become straight porn, because it's there for a specific audience.