Yushiro & Takeuchi friendship headcanons
--Takeuchi got through the final battle relatively unscathed, so he is quick to check up on Yushiro in the aftermath. Having just lost Tamayo and still being overwhelmed by everything, Yushiro just wants to hide and be swallowed up by his emotions for a while, so Takeuchi's company was initially unwelcome, but it turns out to be really good for Yushiro and he unloads more than he thought he would. Takeuchi is a little confused and can't put all the pieces together, but he it accepts it pretty readily.
--Takeuchi continues to enforce his friendship and company upon Yushiro, even once Yushiro insists he's fine by himself (with Chachamaru, whom Tamayo especially left to him). Takeuchi can't be dissuaded so Yushiro gives in and lets him hang around.
--If there's one thing Takeuchi knows about demons, it's that they are ravenous for human flesh, so it finds it concerning that Yushiro never seems hungry, so this leads to Yushiro explaining why he's a special case who subsists on small amounts of blood collected in ways that don't harm humans. He doesn't like that he has to consume it at all, though. Takeuchi offers his own blood again; because he was a strong Breath-powered swordsman, consuming his blood would mean Yushiro could subsist on even less blood. Yushiro refuses because he'd rather pay poor people who need the money; Takeuchi has a Corp pension and doesn't need it. (More so, it's because Yushiro would find it too weird to consume the flesh of someone he knows personally.) This is an ongoing bit in their friendship, Takeuchi continuing to offer and Yushiro continually refusing.
--Takeuchi takes up painting (based on a Murata-related headcanon stated in this one-shot about Murata & Giyuu finally getting dinner together), and he's eager to show Yushiro one of his early works. The most beautiful thing he could think to paint was a sunrise, for it was always such a long-awaited moment throughout many battles Takeuchi fought while in the Corp. Then it occurs to him that Yushiro doesn't get to appreciate such a beautiful sight, which is why he wants to give him that painting. Yushiro, too much of a tsundere to accept it, snaps back that no sunrise could ever be as lovely as Tamayo was. Takeuchi, not offended, sadly states that he never saw Tamayo, so he wouldn't know. Now in an awkward position for having snapped at someone who did a nice thing, Yushiro has to follow through and attempt to show Takeuchi what Tamayo looked like by making a painting of her. Yushiro has a natural talent for it, and Takeuchi is stunned and praises his skills, but Yushiro is frustrated by not having managed to capture her beauty or essence. He has to try painting another. And another. And another. And another.
--Since Yushiro has already lived a long time, it's hard to see Takeuchi as an equal at first; he seems like a small child. Little by little, it's like watching Takeuchi grow up. For instance, one night Takeuchi happily announces that he's courting the daughter of an old wisteria house who he was always sweet on, some months later he's heartbroken because she was only dating him out of a lingering obligation to the Corp. Yushiro winds up falling into a lot of self-reflection about how hard it must had always been for Tamayo to see him as anything more than a child, for the gap between them was so large that even feelings as deep and sincere as his own could never overcome it. This is around the time Yushiro starts really accepting the companionship of Takeuchi, Tanjiro, and Kiriya (whom he sees like more of an equal more quickly than he did with others, seeing as Kiriya has experience beyond his years than closes the gap Yushiro feels with others).
--Takeuchi, despite being busy with the never-ending affairs of the human world and eventually raising his own family, always makes sure to pop in on Yushiro, for he knows Yushiro will never go out of his own way to seek company. It has to be forced upon him. Yushiro acts annoyed when Takeuchi visits him, but he is always a gracious host and they spend hours talking together. Chachamaru says hello and accepts some petting from Takeuchi but typically stays on Yushiro's lap. Yushiro doesn't drink it, but he serves Takeuchi black tea in fancy dishes, and they sit around on velvet chairs in a low-lit basement filled with Yushiro's paintings. Takeuchi never stops with his outpourings of praise and wonder for Yushiro's talents.
--Takeuchi brings Yushiro new copies of "The Legend of Zenitsu" so he can laugh and be entertained by Yushiro's scathing reviews of them. Takeuchi doesn't know this, but Zenitsu brought out an inferiority complex Yushiro can't stand to admit even to himself; it drives him mad how Zenitsu could paint Nezuko with such perfection on a first try, and in his defensiveness he insists it's because Zenitsu has the model to look at. Yushiro pulls from years of dedicated observation that has honed his memory, so their works can't even be compared (or at least, that's what he tells himself).
--Takeuchi eventually falls ill, and Yushiro goes out of his way to pay visits to him. Takeuchi tries to stay positive about it, but the frustration of feeling himself get weaker and weaker and his own inescapable mortality do get to him from time to time. He tries to be as brave as the people who didn't survive their battles in the Corp, but it's hard. He jokingly insists that even though he's weak and wouldn't make for an appetizing meal anymore, he wishes Yushiro would just eat him for his own sake now, if it gives Takeuchi some means of living forever. But that's all it is, a joke. Yushiro, having been in Takeuchi's position before, is heartbroken to watch him go through it, but admires Takeuchi for handling it so much more bravely.
--He's not able to say so at first, but eventually Yushiro is able to open up and talk about his own experiences with illness, and how he would never wish it upon anyone, he has no regrets about being a demon, for even without Tamayo, he still has a zest for life.
--It's a long decline, but Yushiro hangs around as a hospice nurse, and especially as a friend. By this time, he and Takeuchi truly feel like equals. After Takeuchi's peaceful passing, Yushiro doesn't really keep in touch with them, but he keeps a special eye on on Takeuchi's descendants.
