Thematic issues. Why all the sci fi.

[Rosenstrauch]

depending on your defination ff1-ff3 rlly didnt

Final Fantasy 1 has a tower where enemy encounters frequently feature robots, culminating in the Warriors of Light using a teleporter to access and orbital space station. The "secret boss" encounter in that area, on the bridge before you encounter Tiamat, is the WarMech/Death Machine, whose strongest attack was called "NUKE" in the original translation. The Death Machine is in FFXIV, by the by—it's a enemy mob in both Bozja and Garlemald.

Final Fantasy II has an entire sequence where you board the Dreadnought—an homage to the Death Star—with the intent to sabotage it from within. One of the neat things about it is that, while the GBA/PSP remake/compilation of I+II restyled the space station in FFI as a flying castle, FFII turned the Dreadnought into this behemoth, complete with anti-air batteries and a mechanical claw for seizing smaller airships.

Final Fantasy III... There's a submarine? There's an ancient, technologically advanced civilization? Most of the advanced stuff you see here is just crystalpunk, though.

And just for fun:

IV: The Tower of Babil is an interdimensional elevator whose interior is full on sci-fi. The Red Moon is literally a space station the size of a small planet, which you get to via a starship using the same tileset as the Tower of Babil for its interior. There's also the Tower of Zot, and this is the first Final Fantasy to interpret the Iron Giant enemies as gundam-esque machina. This game is also the origin of Alexander in the form of the Giant of Babil—a bipedal machina so enormous it can walk over mountains. The sequel also introduces the True Moon, which is an even more advanced space station able to eat planets.

V: There is an entire clockpunk civilization that seemingly predated the planet's sundering, as a significant portion of it wound up inside the Interdimensional Rift. This is notably also the origin of Omega, a series staple.

VI: May well be the original of the term "magitech", and is a major source of FFXIV's Garlean warmachina designs. The Ultima Weapon makes its first appearance here as a biomechanical monstrosity.

VII: Firmly Dieselpunk and sci-fi.

VIII: The Gardens. Esthar. The bloody Ragnarok. The Ultima Weapon makes its second appearance here, once more as a biomechanical monstrosity.

IX: Terra.

X: I heard you like football and water polo, so we combined them into a single sport where the field is a gigantic anti-gravity sphere of water. It's also a little surprising FFXIV hasn't mined FFX's remaster for its large number of warmachina. Notably, the sequel's final boss is Vegnagun, a warmachina whose ultimate attack is... well. Spoilers for FFX-2

XI: Haven't played, but I wouldn't be surprised.

XII: The literal first boss of the game is a one-man airship, looking even more sci-fi than anything in FFVI. The Empire as a whole loves its futuristic technology, and the game has not one, but two homages to the Death Star in the form of the Dreadnought Leviathan and the Sky Fortress Bahamut, the latter of which has you fighting the Emperor alongside a Darth Vader analog who betrays him in the game's final hour. (Funnily enough: II also had a Darth Vader analog, and both characters had a familial connection to someone in the player's party).

XIII: Pick an Allagan machina. Any Allagan machina. There's a 90% chance it came from this game, with the rest of Allag's aesthetic being stylized to match them when it wasn't cribbing stuff from FFIII instead. Though given that we call that aesthetic "crystalpunk" now, it's also technically sci-fi!

XV: I'll just let Gary Numan sum it up.

XVI: Haven't played, but I've heard Omega is in it in some capacity, and that's all I need to know.