Well, Lilia Vanrouge's a character from 'Twisted Wonderland,' right? So the fanfiction for that pairing, 'Lilia Vanrouge x reader,' tends to be concentrated on platforms where the fandom itself is really active. A lot of the dedicated and original stuff is over on Archive of Our Own, or AO3. The tagging system there is robust, so you can filter for 'Twisted Wonderland,' 'Lilia Vanrouge,' and 'Reader Insert' to find a bunch of works. Writers on AO3 often put a lot of care into those stories, crafting scenarios that explore his mysterious, caretaker-like yet chaotic nature. Tumblr also hosts a surprising amount of it, though it's sometimes in shorter, more immediate forms like drabbles or headcanon lists that can spark longer narratives. You might find writers linking to their full works on AO3 from their Tumblr blogs.
It's worth checking Twitter, or X, as some artists and writers will share snippets or threads there, using hashtags like #TwistedWonderland or #LiliaVanrouge. The thing about reader-insert fic is that it thrives in spaces with strong community interaction, so platforms with reblogging or commenting features tend to foster more of it. I've also seen some on Wattpad, though the search there can be a bit more hit-or-miss compared to AO3's precision. The tone of the stories varies widely, from fluffy domestic scenes with him cooking something dubious to more plot-heavy adventures tapping into his long history. I usually find the most consistent quality and volume by starting with AO3 and then following authors to their other socials if they have them. Seeing how different writers interpret his playful teasing mixed with that deep, ancient wisdom is half the appeal, really.