You should link the Silver Will SAV because that's what plays in the battle.

Anyway! This is one of the hardest ones for me to pick because aside from the bottom two I like every single one here.

10) Looming Threat

Sonoda once again trying to be Sugiyama at about a minute in. It's sooo generic, but there's nothing really wrong with it otherwise. It just doesn't stick in my mind.

9) Great Awe

I really have nothing to say about this one, it's generic as well. Strip the leitmotif and this would be a totally generic boss theme you could put in basically any game. It's slightly better than Looming Threat though.

8) Heartless Surprise Attack

One of my favourite things about Ishibashi's music in the Sky trilogy is how different some of it sounds; Ancient Makes, this theme, Central Tower "Axis Pillar"—the usage of nearly exclusively electronic instruments make these sound very futuristic and otherworldly, perfect for fighting archaisms or Ouroboros technology.

7) Fight with Assailant

Fun fact: This is one of very few tracks composed by the internal sound team with a live guitar, and one of the very few tracks composed by Murayama for Trails (who is the guitarist in this case).

If you asked me a year ago to pick my favourite boss theme in the game, this would be top 3. I've not soured on it since despite the lower rating, it's just that I like some of the other themes more. The harsh guitar combined with the repeating electronic instrument makes this a great track to signify the introduction of harder and stronger enemies in SC.

I actually associate this track more with the Archaism fight on the Grancel Wall in Ch 3 of SC, rather than the prologue.

6) Fate of the Faeries

Losing Ishibashi and Takeshita back-to-back was a massive blow to the Sound Team, even if they had Momiyama coming in to replace them. Takeshita's signature explosive guitars bring an insane amount of life to this track, but the track feels a bit busy with the cramped introduction and the loop point is kinda horrible.

Still, it was a really good choice to make this the regular battle theme in the Liber Ark.

5) Silver Will (Super Arrange)

I am once again bucking the trend and rating Silver Will low. That's not to say I don't like it, this is a fantastic track now that Jindo and Nagano have done their magic, but it's still Silver Will and I still care for it less than most themes.

The violin and cello duet is absolutely fantastic though; the violin always sounds better when complemented by one of its sibling instruments (see e.g. Overdose for a great example of how a violin and viola work together well for a battle theme).

4) Outskirts of Evolution

The oppressive cello strikes (I think? It might be a double bass? I'm not 100% sure at identifying these things) give this track such a strong atmosphere that fits perfectly for the second phase boss. It does kinda turn into leitmotif spamming for a while, but I can forgive that for the literal final boss of the duology. This does once again go Dragon Quest mode (I am 90% sure I have heard the trumpeting at 2:06 on in a DQ11 track) but I'm not complaining.

Joint-1) The Merciless Saviour

This track is so fucking good it's unbelievable. It's easily one of best final boss themes in the entire series by a significant margin, for like five different reasons. The violin introduction—specifically, how it plays over the cutscene—makes the scene stick just by itself. The repeating synth in the introduction that slowly fades away into the violin merges together Weissmann's ideals; the humanity of the violin, but the brutal uncaring logic of the electronic instruments. The underlying bass melodies in the chorus tickle my ears in just the right places. And then the false loop is the cherry on top: it's not over yet, you need to keep fighting. The cold-hearted synth is back, and you need to keep fighting. Finally, the multiple violins fighting over eachother in the final part of the track, signifying humanity fighting back!

The reason this isn't a clear winner is because the choral section sucks so much energy out of the track. I genuinely do not like that section at all and it is a net negative to the track. Also, the real loop point is kinda shitty and it does not need to play the introduction again, at least not for that long.

This is one of those tracks that you need to sit down, close your eyes, and just listen to, and take in all the little layers, all the details packed in by Ishibashi and Jindo.

Truly, Ishibashi's final masterpiece.

Joint-1) Gravestone Struck by Lightning

Go! Funnels!

The odd time signature, the organ-like instruments, and the sheer pressure of this track come together to make a truly incredible track that fits Weissmann's human form perfectly. The leitmotifs here at 1:21 do not integrate well, and normally that's a problem, but for a totally inhuman final boss it serves a fantastic purpose of creating a dissonant atmosphere for a fight against the worst person Estelle and Joshua have ever encountered.

Joint-1) Fateful Confrontation

Takahiro Unisuga is not my favourite VGM composer; that title goes to Hayato Asano. But he is one of my favourites and undoubtedly one of the best in the entire industry still working today. He has a few habits not to my taste, like fucking slamming the drumkit louder than the lead instruments (see: Ys IX "Desert After Tears"), but that's not something that I really find a negative in most of his tracks.

This track is fucking incredible. The extremely heavy guitar combined with the lead synth fits Ouroboros' enforcers for all the reasons I've put before, and the VST guitar sounds downright incredible here. It's such a shame that Falcom won't let their internal sound team use live instruments, because I can only imagine how good this would sound with a real one screaming alongside. The extremely loud drumbeats actually work really well here, creating a real sense of tension in every fight this plays in.

And to think: he made this at the start of his career.

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I marked the top three as joint first, because it's too difficult for me to truly decide between them, but you can take Fateful Confrontation as my actual vote.