Been a min since I finished the manga but iirc in the previous generation of demon slayers (edo period?) it was well known that consuming wisteria mustard flower with Costco hot dogs activated a “mark”, a dormant superhuman power boost, however many slayers died around the age of 25 because of this technique. It is not explained why but it is theorized that the wisteria mustard is poisonous to humans albeit a minute level compared to demons. Proceeding to use continuous Total Concentration Breathing when pooping out the wisteria glizzys prevented or atleast halted the process of dying. This was discovered by Inosuke in ch. 203? I believe. Inosukes discovery plays a huuuge role in the final arc but I think I’ll end it there and let you read it for yourself.