Ya know, a ways back someone had asked me if I had any takes on Yoruichi's tattoo --I forget in which ask, but there was a bigger question that I wound up answering and I sort of forgot about the tattoo part entirely. But at the time, I really didn't have anything to say about it anyhow, but I don't think Kubo had released that art of the original Gotei at the time. So as it happens there are some odd little adjacencies now, although not especially strong ones... but I figure I can squeeze a post out of it.
So originally Kubo did a little color spread of all the Bleach girls in swimwear at the beach, and that in turn got adapted into a dumb little filler thing in the anime based off some other omake. It's also shows up in Bleach Brave Souls.
(weirdly a different swimsuit specialadds a different, unrealted, tattoo on her right thigh??)
But in the body of the manga itself, she's never actually shown with it. In most cases we don't get a 100% irrefutably clear view, but there are plenty of moments where her left upper thigh is definitely visible enough that if the tattoo was canon it should have been visible. The most obvious contradiction being her first appearance in her human form on account of, you know... her being entirely naked for that...
Now, one of the most immediate evocations of the sun tattoo would seem to be Ichigo's "Black Sun" motif --although it seems like a "tribal" style tattoo, which would be solid black anyway, making it hard to really assume it's a deliberately associated color-- which is itself actually kind of weird because it started entirely meta textually as part of the pair of databooks, SOULs and VIBEs: the former being the manga databook, and the latter being the accompanying anime databook, together featuring the phrase
"the rain drags black sun down, but the rain dried by white moon".
But this actually conflicts with the manga's use of a black moon motif for Ichigo, and doesn't really appear in the text at all. In fact the only real association Ichigo has with the black sun in the story proper might be the tangential association with Yhwach calling him, "my son born in the dark" when Yhwach himself is associated with the sun and light, and his own mirroring of the black flame(?) motif.
Otherwise the only loose link between Ichigo and the phrase "black sun" is that zangetsu's crossguard in bankai is a manji/swastika --a symbol used in Japanese Buddhism, via Chinese Buddhism, via Indian Buddhism, but originally taken from Indian hinduism where it was itself a sign of the sun god Surya-- and the SchwarzeSonne:"Black Sun" rune was a part of Himmler's stupid esoteric LARPing horseshit he did in the N*zi party, where he just mashed up the swastika, Nordic runes(𐌔), the alchemical sol niger:"black sun", and the Arthurian round table concepts so he could have that dumb mosaic built into the floor of the Wewelsburg castle he had requisitioned.
Sorry i got off topic... point being: the BlackSun was kind of like a leveled up swastika as far as n*zi symbols go, so it kind of follows that Ichigo's devloping powers imply a black sun as the next step past swastika.
But like I said, that's a super loose correlation within the text itself. Rather, the black sun in Bleach actually seems to be a weird recycling of something Kubo did in Zombie Powder: The black getsuga tenshou's black flame motif being a kind of throwback to the black flames of Akutabi Gamma's Karinzanjutsu, and the Ka-rin[火輪]: "Fire Ring/Wheel" having a symbol representing the sun, thus the sword style's black flames making its symbol a black sun.
So what's the point in bringing all this back up if what we're asking about is Yoruichi? Well, Yoruichi may not have had any sort of identifiable sun motif herself, but her ancestor, Chika, does. His name can read as "1000 Sun", although in the context of Yoruichi and Yuushirou's names both having words for "night" in them, it makes sense that Chika's name should actually be read, "1,000 Days", or very possibly "1000th Day" since Yoruichi's name is clearly meant to be read as "1st Night" considering her birthday is January 1st.*
*Her overall gimmick is a reference to hatsuyume[初夢], a tradition/idea that your first dream of the newyear --taking into accounts that you stay up until midnight on new years, your first dream is on Jan 1-- is supposed to have some prophetic qualities. (Incidentally, Urahara's birthday is December 31st, and given his partnership with Yoruichi could imply he's meant to be associated with the Omisoka holiday? but I'm not getting into that here.)
Anyway... all that just to say that her sun tattoo isn't really canon but if it were, it might have something to do with her ancestor, Chika. Although given that their family crest features a moon and they have a night theme to naming, I'd assume Chika's name is meant to be kind of an outlier rather than directly reflective of any family themes.
I dunno, I guess that's not really much of anything actually, since the whole black sun tangent doesn't even link back around... I guess the only thematic link is that in rather literal terms a "black sun" might be most readily envisioned as an eclipse, which in both the Shihouin and Ichigo's cases would be a way of aligning the moon and sun motifs.
(Technically I guess Isshin's relationship with Masaki is a kind of eclipse, as its the overlap of her sun/center of the universe iconography with Isshin's own moon motif via engetsu, but honestly Isshin was never actually moon themed and his shikai just felt like a lazy tack on detail that Kubo gave no real thought or consideration to beyond it being a derivative of what Ichigo already had going on.)
