The first stanza is mainly about both their individual traumas and shared traits, whereas the second and third talk about them slowly opening up a bit more. A and X already have a great deal of trust in each other in the main story, and I see their relationship as both a sort of qpr and a possible courtship. Labels are difficult – point is, they do care for and like each other already, and are now starting to go deeper. The last two stanzas are about that.

blood of the crown // i can't wash it off // a whisper among the hollow bones:

(this has spoilers for both of their routes!)

Blood of the crown ties to both A’s blood connection to Crown Piruz and X’s hatred of the very same Crown, because his actions led to the deaths of X’s entire village, so X has been hunting down the people Crown Piruz ordered to burn the village.

Hollow bones does in part refer to the deaths caused by both of their hands – A in relation to how they blame themselves for their father's countless murders, and X’s own assassinations. Aside from that though, hollow bones are very common in birds, which is something (at least I personally) associated with both A and X (look at past official asks for this lol).

for one of fire // i am a liar:

Fire in ATOC is connected to the truth! It’s endlessly fascinating to me how X hides their secrets behind a veil of honesty, when they deflect so much and have zero qualms about lying. It’s the same for A – it’s not that they’re dishonest, per se, but they are actually. Like, they haven’t told X and R about them being Crownsblood. When X literally has the mot hatred for their father. Not that A knows that, because they’re lying too. Absolutely fascinating dynamic.

does the water sooth you?:

Water is A’s affinity, representing self-reflection!! Reflection is also briefly mentioned in the first stanza (sins of so long ago– // are reflected within my heart. // just as you are) so.. idk, do what you want with that

you don't have to let me in // just know that i'm still here:

This is a Florence + The Machine song, Hiding. One of my personal favourites from them, as well as a song mentioned by the official tumblr before I believe? That was mostly a coincidence since I was listening to it as I wrote and remembered it was quoted somewhere, making me jot it down. It is also rather probable I'm imagining it, but there's the thought process behind this line haha.

beneath that green hidden between smirks // even further down; in the brown earth // something is blooming, something incorruptible:

Aside from the correlation with eye colour (X with green eyes; A with hazel, aka green and brown), this line is about a lotus. Roughly paraphrased, X said that A was impossible to bribe, and many other characters mention that A is hard to corrupt. Which is something interesting to me considering their background of being raised so privileged, or perhaps it’s a result of that very same upbringing. Lotuses are also associated with growing even in the most dirty environment, which fits both of them pretty well imo.