How would you built FF7 characters in D&D?
Is Cloud a fighter?
Barrett a Warlock with Eldritch Blast?
Depends on what's important to you about them, but if I was going to do it assuming (a) no new rules and (b) focus on Vibes over Strict Accuracy, here's what I
might do...
Cloud is a Fighter. Use a Greatsword. His most iconic ability, Omnislash, is just a LOT of attacks, so Action Surge -> Attack at high levels would represent that pretty well. I'd be inclined to consider Eldritch Knight so that we can weave a bit of spellcasting in there - materia, or certain limit breaks like Blade Beam, might be best modeled that way.
Barrett is a Ranger. His gun-arm is just a bow or crossbow (or, if I could purchase a firearm, I'd use that). Nature-themed magic works well with his Planet-centered ideology. I'd probably go with a straight Hunter with no new rules.
Tifa is a Monk, natch. I'd go with Open Hand.
Aerith is a Cleric. Definitely a Thaumaturge. Healing is her main niche, so I'd go with the Life domain.
Red XIII is a Barbarian. Going from the remakes, Rage can be a good vibes-based replacement for Vengeance Mode. I'd probably go Berserker (though World Tree is tempting!) and fluff the axe as tooth and claw.
Cait Sith is a Warlock. Mostly to get the Mog as a familiar via Pact of the Chain. I'd probably go Archfey for the patron, since there's some trickery and silliness there. As a D&D party member, I don't think I'd be able to secure the whole "tiny creature who mounts a Medium familiar constantly" vibe, but I think a Sphinx of Wonder could be refluffed as a moogle, and if I wanted to REALLY lean into it, maybe I'd be a tabaxi. Though I could also go with my PC being the mog (an autognome? a warforged?) and the familiar being Cait Sith (still Sphinx of Wonder probably, though could also be spirite, imp, quasit, or pseudodragon), which could be a lot of fun.
Cid is an Artificer. Cid is a bit of a challenge, but Artificer has the right vibe. Defenses are A+. I can cast the
Jump spell, so got that covered. My spells are definitely mechanic-themed. A returning weapon helps me huck my spears. I'd probably go Armorer, but I could see an Artillerist, too. The important things are that he swears a lot and has a failed project he's blaming someone else for.
Yuffie is a Rogue, and I'd run her probably as a Thief. I could see a case for Arcane Trickster, though. I choose thief mostly for the thematic ability to pick pockets as a Bonus Action and the obsession with magical items that can turn into Use Magic Device.
Vincent is a Druid. I could see a few different paths for Vincent, but emphasizing his transformations means Druid to me. We don't need the "plants and animals" magic, but we can use the fire and elemental spells to represent shooting with a gun (Produce Flame, Starry Wisp, Ice Knife...), and we can use beast statblocks to represent his various transformations. I'd go Moon to get the most fearsome forms - this is not a character who uses wild shape to turn into a mouse or a sparrow, it's all bears and wolves (flavored as horrible monsters).