In my story, the main character gets help from / saved by two complete strangers. They don't tell the mc who they are or what they are doing, they just helped the mc out of kindness and disappear just as fast as they appeared.
Later, at the very end of the story in the final chapter, I have these two characters come back into play and reveal a twist about them. Just as an example, let's just say that they are the kids of the legendary hero or something (which is NOT the mc, btw.). The villain is actually defeated at this point, the two simply come back to finish off the villain for good, so he may never return.
Could this be a bad idea for these characters? Sure, a bit of mystery is intriguing, but I feel like I don't show enough of these characters, since they only appear in the first and last chapter, so they might appear like asspulls to some. I get the feeling people won't care about these characters, given how little they know about them, even if I spend most of the last chapter focusing on them and what they did behind the scenes that affects the main storyline.
What I did to kind of solve this issue is reveal things over the course of the story that indirectly gives more info about these two characters, without ever mentioning them. For example, someone might mention how the race, which the legendary hero belongs to, have red eyes, and the two mystery characters have orange eyes, "diluted" from interbreeding. Still unusual looking for a normal human being, but not as noticeably strange and it's not unique to the hero's children, but it does give a little hint towards their identity.
In fact, when I show those characters in the first chapter, I drop a lot of hints like this without the reader even realizing, as they are hints for things the reader couldn't have knowledge of at the time when they start, but the reader does gain that knowledge over the course of the story. The reader (and the mc) doesn't know about the red eyes yet when they first see the two characters, but finds out about it later. Not to mention, since the two characters are gone so fast, the reader might forget about them and not even realize they're getting hints to those characters.
Should I show these two characters more often instead?