This reminds me a little of the Final Fantasy 6 opera scene, not so much the music itself but the context of involving a performance art like music in with the battle mechanic. In both instances, a music performance was a means of advancing the main plot and not relegated to a fun sidequest or mini-game. FF6 was probably the first console game to do it, so in the memory of people like me a comparison to Octopath is inevitable.
Here’s the song in real time, during gameplay, with the voiceovers, etc. “Song of Hope” song starts a bit over halfway through, after Dolcinea, the boss, shifts into her final form. It’s interesting that she transforms into a singer where her first form was more fighting-oriented. Usually, boss forms will get more menacing as the fight progresses.
Like “Song of the Ancients” from NieR, “Song of Hope” features a made-up language, though to me it sounds close to English with some Latin thrown in.