I'm embarrassed to admit how far I scrolled your blog because I saw you mention having a post about why you think the Marked Slayers lived past 25, haha. I'm always curious to read what other people think of that because I also see them living longer, just maybe not "full" lives, like maybe to their 40's-50's. Couldn't find it though 3: Gonna stick around though, great posts <3
I remember now it was a comment i replied to and not a post !!! But worry not , i shall explain in a post right now ✨✨
WHY I THINK THE MARKED SLAYERS DID NOT DIE AT 25
We know from Lady Amane that in their records, all the slayers from the Sengoku period that awakened their mark (except for Yoriichi Tsugikuni) have died around the age of 25. More explicitly, her words were - "they did not live past 25". Which, if you take it literally, means they died young, younger than 25, but not at that exact number. Which makes me believe that the slayer mark does not magically make you die at 25 years old - it damages your body enough to die young - younger than that. So here come my hypothesis :
1. GIYUU AND SANEMI AWAKENED THEIR DEMON SLAYER MARK THAT NIGHT AND ONLY USED IT FOR 5-6 HOURS. They did not use their mark for a long time, so their body did not have time to be damaged so much as to die so young. What i mean is that the slayers who used the mark their whole lives (maybe even 10 years if they awakened it at 15) - they died at 25 because their body could not take it anymore, and it makes sense. But the two Hashira used the mark for 5-6 hours, only one night, for the final battle - I don't think they would die so young for the few limited hours they used the mark.
2. TANJIRO - now that is a different discussion. He used the mark young, and for a longer time than them , for several fights. But let s make a calculation - Tanjiro manifested his demon slayer mark for the first time in the Entertainment district - against Gyutaro. After this came the recovery period, the Swordsmith village arc, another recovery period and the Hashira training - these are a few months compiled. Let's say 6-7 months, because in the infinity castle it wasn't winter yet. Tanjiro used it longer, yes, but nowhere near the amount of time they did in the Sengoku period, so i think it also wouldn't affect him so much.
3. Tanjiro is considered the reincarnation of Yoriichi Tsugikuni - we see this through his breathing style, his family history, his earrings, and most importantly, the inherited memories of demons who see Yoriichi in Tanjiro without even knowing who he was. Yoriichi was the only slayer of the Sengoku period who lived with his mark up to 80 years old despite having it since he was born and using it his whole life. This reinforces that Tanjiro will certainly not die at 25.
Yes, probably instead of dying at 70 years old, Tanjiro died at 50 and Giyuu and Sanemi at 60 - VERY rough estimate. But i really don't think they died at 25 or anywhere near that young.
4. Another theory i saw circulating which might also be the case - the demon slayer mark is compared to a "demon crest" and it is considered a curse. A curse tied to Muzan, that will make the slayer die so young , and we can consider that if Muzan is dead, and the Ubuyashiki curse is lifted as well - the demon slayer mark will not kill the slayers anymore either. There are no demons around, which might even mean that their demon slayer marks don't even exist anymore. They can't manifest them anymore, because there are no demons to kill.
I hope you enjoyed my theories and explanations and i will really die on this hill that after everything said and done the two remaining Hashira and the chosen one will not die so young because of the marks they manifested (and only used for a few hours or a few months respectively)