Lae'zel. In fact, isn't there literally a quote about Lae'zel breaking her chains? From Vlaakith.
Shadowheart. Breaking her chains from Shar.
Wyll. Breaking his chains from Mizora.
Dark Urge. Breaking his chains from Bhaal.
Karlach. Breaking her chains from Zariel.
Gale. Breaking his chains from the orb.
It's a theme throughout the entire cast of characters.
Entirely this! I always interpreted I Want To Live as a song for all the party members, who share the theme of breaking chains either literal or mental and wanting to live in spite of the obstacles before them. Astarion wants to be free and have a chance to finally live, but Wyll wants to be free from Mizora and not be damned to the Hells as the reward for his sense of duty, Shadowheart wants to live and experience more than grief and loss and stifling servitude, Karlach wants to live despite the engine as a ticking clock, Gale wants to live despite Mystra's mandate of suicide, Lae'zel wants to be more than a sacrificial lamb for Vlaakith and can finally experience life beyond that of a child soldier, Durge wants a chance to be themselves more than the Urges... etc.
Okay, I agree, somehow the theme of "breaking chains" is evident in all the main party members, except Astarion had heavier chains than the others. Well the subjective perception of a favorite character is when his story comes to the forefront, and that's how you can look at any companion. About the will to live - not everyone expresses it so explicitly. Karlach regularly expresses her willingness to die just to avoid going to Averno; only in the dialog after Gortash's death does it become clear how much she wants to live, but not to survive at all costs, but to live the way she would like to live. Gale scares with his "suicidal attitude" quite significantly, in the first playthrough without spoilers, it seems that it is Tav who tries to talk him out of it with all possible lines and, to the great relief, they succeed. To see his will to live, you have to look at his reaction to Tav, who agrees with this universal self-sacrifice.
'Your blood like wine' is pretty Astarion (or Durge), and reading our own interpretations into the songs is a free country - heavens know I've done it with several already. But claiming the song belongs to him and that every other interpretation must be cope/Mary-Sueing is myopic towards all the other characters. BG3 is very thematically tight and the origin characters share a lot with each other. I also don't think 'invite me in' has to strictly be about vampires when the metaphor is just as plain for two people getting to know each other and letting each other past each others' walls - which is, again, something that happens with all the characters.
"Oh darling, get me drunk and make me feel" after "Your blood like wine" - Astarion drinks Tav's blood and it makes him feel better ("make me feel"), and we come to Rivington just after the Dark Lands, where Astarion practically did it all the time, since edible enemies are encountered there only once or twice
. I'd like to add that I changed my original opinion after ldo58's explanation, and after reading the tweet at the link.
Though on the topic itself - agreed that The Power and Last Light are both gorgeous, the ending credit version made me cry that first time, but I've gotta push a couple of other favorites from the soundtrack.
I would also like to add Raphael's awesome song. The fight with him thanks to this song becomes incredibly epic and exciting (I replayed it several times for fun). On the downside - the constant playing of the same song in the tavern. The song is not bad in itself, but because of the constant playing starts to get very boring, it would be great if in elfsong tavern on vacation played different tunes, including we could hear "I Want To Live" again.
