Male Layikani have very few fire marks on their necks and temples. As a result, either the mark does not sparkle after the neurotoxin from the Ngiki alga is injected, or the reaction is less strong, so that the symbiont dies when it tries to penetrate the Layikani's body below the male collarbone.
While the lack of reaction to the fire marks is still the harmless variant and the man only suffers mild and short-lasting symptoms of paralysis on his face, the second variant, if lucky, leads to immediate death. In the worst case, the failed symbiosis leads to degenerative nerve damage and vegetative state.
Over the millennia, there were mostly male doctors, scientists or alchemists who have attempted to develop technologies to enhance the fire mark or spark reaction and mitigate and heal nerve damage, or who have explored other ways to fully utilize fire magic.
A really great submission for your prompt, and it feels like you manage to tell so much about Layida culture with this and the Spark Condition alone. Truly sounds like everything could turn on it's head the day they succeed in developing a working enhancer.
Thank you for liking my solution to the prompt and yes, you're right, it had so much influence on the development of the Firewalker culture while also providing so much potential for conflicts. That's why everything really has to remain top secret and I hope they never find a real solution, because I could imagine that it wouldn't end well for the women.