The second of the three parts of 1-1 "Opening Theme" plays (the first part is used at the title screen) as introductory text and glimpses of various locations are shown on the screen.

Note that I'm using the "Kefka's Domain" English OST release track names rather than the original Japanese ones, partly because they should be more familiar and partly since that's pretty much what I was already using when it finally occurred to me to double-check the actual names.

The music fades out, replaced with a wind sound effect. Two soldiers and a girl enter riding simple mechs. The soldiers wear brown armor with blue gloves and boots, which appears to be a standard uniform. In contrast, the girl's uncovered green hair is in a shoulder-length ponytail, and she wears a red outfit with purple epaulets (shoulder armoring).

Note that the JP version doesn't even bother naming the soldiers in the dialog here. They're just that unimportant.

Since 幻獣 (genjuu) isn't a simple term, and I like the way it sounds, I've left it as is. The meaning does deserve an explanation, though. 幻 most likely means, in this case, something that is so incredibly rare that it's simply not realistically possible to prove either that it does or that it doesn't exist, something like "fabled". 獣 means "animal" or "beast", and probably refers to the fact that they aren't human, but this doesn't necessarily mean they aren't sentient or intelligent.

Official translations have handled the term differently in various games across the years. I know that FFIV (2 US) mostly calls the same thing "summoned monsters" in accordance with their primary gameplay function, while FFIX takes a more succinct and exotic approach with "eidolon", which seems to have more or less become the standardized version since. It's probably what I'd use if I were translating the game now.

"That" probably refers to the girl, considering where the conversation goes. It seems she's treated as a secret weapon.

Though not quite as vague as "thing", かざり (kazari) doesn't do much to describe what's on her head, as it's a generic term for anything decorative.

They head towards the town. As the mechs lumber over the snowfield, the opening credits roll, and the third and final part of "Opening Theme" plays.

The town lies nestled into the bottom of the cliffs. Snow covers the ground, melted in numerous places from the heat of complicated machinery. The houses seem relatively modern. No music plays; only the sounds of strong winds are heard. The soldiers enter from the south and start into the middle of town.

Put everyone in the back row to reduce damage taken. The special attacks they all use ignore row, and are overpowered enough for now that it wouldn't matter much even if they didn't.

While the generic soldiers have no special abilities, the girl can use some magic (Flame and healing spells), and is the only one with MP (magic points). She additionally has more combat experience.

As the mechs rumble through town, local Guards, and sometimes a canine Silvario or two, attack repeatedly. Those poor fools.

1-5 "Battle Theme" plays during normal battles, and 1-6 "Fanfare" normally plays after victories. Aside from underscoring the incredible combat advantage the mechs give the attackers, battle also reveals that, in addition to magical powers of her own, the girl is better able to use the mech's abilities, and can unleash a variety of attacks that are beyond the skill of the ordinary soldiers.

Guards near the mine entrance bring an imposing-looking pair of Megalodolks, but they should pose no real threat.

Finally, the invading group reaches a mine entrance in the back of town.

They head in. 1-2 "The Mines of Narshe" plays inside.

At a save point in the mines...

They soon come to a barrier. One of the generic soldiers steps forward.

He breaks down the barrier, but a local guard steps out.

Thanks to Kahran042 for suggesting "Ymir", a frost giant central to Norse mythology. Japanese usually renders that name as ユミル, but it seems close enough, and the NA version of the GBA remake also uses the name Ymir. A whelk, on the other hand, is just a kind of large snail with a pointed spiral shell.

Boss battle time! 1-24 "The Decisive Battle" plays during boss fights, except for a few that are special. For whatever reason, most boss battles in this game don't give any experience points (very useful if you're attempting a low-level game). Since the designers apparently felt generous considering the game has barely started, the soldiers give out a hint first, with excessive jumping and arm-waving...

こいつ (koitsu) doesn't translate very well. It basically means "this one" or "these ones", and tends to be somewhat derogatory, or at least not respectful. It generally refers to living things, though I've also seen it used for complicated machines.

The shell counters with powerful (for this early) Thunder magic damage if attacked. Focus on the head instead. The girl's Sorcery Missile works particularly well. The head will periodically retract into the shell...

...which prevents it from being targeted, but also prevents the creature from doing anything unless you hit the shell, so use this time to heal. The head will emerge, making the same noise, before long. Being the first boss, this is an easy fight unless you're careless.

Once the monster falls, the invading force proceeds further in, soon coming to a beast frozen in ice.

After some blue glowing, the game shifts to a combat screen, but 2-20 "Another World of Beasts" plays instead of battle music. The name bar calls the creature なぞのげんじゅう (Enigmatic Genjuu), or Tritoch in the NA release (and while this is the creature's name in that version, it makes no sense to display it yet).

Okay, I'm used to differences between the NA and JP versions, but how you could possibly get anything about anyone knowing anything out of that is beyond me.

The creature glimmers, and the girl, who wasn't supposed to be able to act on her own, steps forward...

Wedge flickers and vanishes. He's just gone without a trace, mech and all.

Biggs flickers and vanishes, just like Wedge did.

The reaction with the creature intensifies. Auras manifest around it and the girl, energy arcs between them, the mech explodes, and the screen goes black...