The royal ball, the one where which would soon be crashed by Ganondorf and his forces, was fast approaching.
Too many words.

Backslash nodded, having picked up the needed gear while listening to her talking (including his Monado replica).
The placing of the parenthetical aside is a bit weird. On first glance it looks like her talking includes his Monado replica.

But before the agents could comment on on the new arrival ...
One "on" would be sufficient.

She would later be found by Violet Link, or Vio for short, who started talking with her about the previous events — and completely failing to ask how she even got here in the first place.
There are some weird tense shifts going on here. She would be found by Vio (in future tense), but then it had already happened and he started talking (in past tense)? Also, it is technically possible that he started talking and also started failing to ask, but the sentence just doesn’t look right to me. It may be better to say "— and completely failed to ask how she even got here in the first place."

HG

... Okay, I don't know what would be the worst for Link. The song which (I guess) inspired the title, or this fic.

And as Voyd said, plot thickens quickly. You realize we all ned the sequel now? Please.

Also, I happen to own the Hyrule Historia and I've read the Four Swords manga; you obviously did your research, because I didn't see any inaccuracies in regards to the canon. Nicely done!