If you're craving a treasure trove of 'Tengen wives' stories, my go-to is Archive of Our Own (
AO3). I get lost for hours there — the tagging system is a dream, so I can filter by fandom 'Demon Slayer', relationship tags like 'Tengen Uzui' or 'Tengen x wives', and sort by kudos or date. AO3 also makes it easy to find explicit content warnings, language filters, and whether the fic explores poly dynamics, fluff, or heavy angst. I usually skim the tags and the first chapter before committing, and I leave kudos and comments whenever a fic hits me in the feels.
Beyond AO3,
wattpad and FanFiction.net host plenty of episodic or long-running takes. Wattpad tends to have more serialized, YA-leaning entries and creative reinterpretations, while FanFiction.net has a bigger, older archive even if tagging is clunkier. Tumblr still surprises me with gems — search the 'Tengen Uzui' or 'Tengen wives' tags and you'll find standalone one-shots, headcanons, and art that link back to hosted stories. Pixiv (if you can navigate it) often has Japanese-language short stories and illustrations that expand the trio's chemistry in beautiful, concise ways.
I also hang out in a couple of Discord servers and on Reddit threads where people share rec lists and translations. A little tip: follow authors you like, check their bookmarks, and use content warnings seriously — some of the best fics are emotionally intense. Finding a favorite writer who treats the characters respectfully has led me to whole new universes, and I always enjoy sending a kudos or comment when something resonates with me.