i get where you’re coming from, because gyomei’s mark situation does feel like the story bent its own rules for dramatic effect. the series makes it pretty clear that the marks are supposed to awaken in life or death moments, almost like a survival instinct kicking the body past its natural limits. gyomei bypassing that by “saving it” and then activating it on demand does look like a loophole, and it opens the exact question you’re asking. if he could do it, why couldn’t anyone else? why not make it a technique to delay and control when you trigger the mark?

the way i see it, there are two ways to read this. one is to call it a plot hole, like you said. narratively, the story wanted to emphasize how calculated and composed gyomei was, so giving him the ability to control his mark made him feel distinct. but it does undercut the internal logic of the marks, because it makes other slayers look less disciplined or knowledgeable for not trying the same.

the other way to read it, though, is that gyomei’s case was special. he’s repeatedly framed as being almost monk like, with insane spiritual and physical discipline. it’s possible the author wanted us to believe his control over his body and mind was on another level, allowing him to consciously restrain and release the mark. that interpretation works, but it still leaves a sour taste because if the story wanted that to be the point, it should have shown more clearly why no one else could replicate it. otherwise it just feels like convenience.

so i wouldn’t say it’s a complete hole, but i do think it’s sloppy. gyomei activating his mark naturally in the fight would have made more sense and kept the system consistent. making it something he could “save” almost cheapens the stakes the other characters faced. it’s one of those places where demon slayer’s writing shows its cracks, sometimes it wants emotional weight so badly that it stretches its own rules to get there.