Ohhhhh, I thought about that lots of times, even wanted to draw my characters in a little D&D AU one day <3
Kim - she'd definitely be a fighter! Give her a sword and she can deal with problems (might get a multiclass level to Barbarian, whenever she sees Aotaka, her Nemesis XD; )
Aotaka - my antagonist. In my Comic he's a Fire Mage, and since the magic in Remember is internal, he'd probably be a sorcerer, maybe with some draconic origin? Heavily fire-based and with Dimension Door and Teleport (every Mage can do this)
Sabbath - she's a Half-Mage, so in theory she'd be a Sorceress, too, however, since she grew up as the child of healers, I'd probably give her Cleric or Druid. Preferrably Cleric tho, because I like Clerics =)
Scy - he's a non-human, insectoid character, his class would probably be Fighter, too. In contrast to Kim, he's a very old soldier and the last of his kind, so he tends to attack from the shadows. Then again he's spent the last 100 years surviving in the wilderness, so he'd probably be a multiclass Ranger, too?
Yumiko - definitely Rogue. If I ever met a sneaky and stealthy dude attacking from the shadows with some kind of creepy magic attached, it would be him. Maybe Assassin or Arcane Trickster?
Kujo - uhm... kind of a puzzle... I mean, he's just a harmless tailor? °/)° He can do some stuff though that's not magic in Remember, would be considered magic in D&D. So... Sorcerer, too, but with Wild Magic. His stuff can backfire af...
For my series, considering the main cast I presented atm, they would make the following party:
Nadhine, although she fits in the stereotypical role of a rogue, she would definitely play as a Paladin. She likes facing opponents right on and protecting those she likes. She would be one of those players that likes to make characters that mirror herself somehow. As for a race, she would play with something big and buff, like a Dragonborn.
Raheem would like to play as something quite ordinary, so that he could understand more the struggles of humankind. He would play as Bard or Ranger, anything that didn't evoke magic at all, so that he wouldn't be able to resort to the very thing he always had in his entire life.
Yami wouldn't play xD he would be the Dungeon Master OR the person that watches the playtime unfold as his girlfriend/ wife is the one that actually plays DnD.
Esther would play as either a Shaman or Druid; those classes are the opposite of what she is in life, as they are carefree, straight forward, no-nonsense and can bend elements and even animalistic instinct at their own will, which would give her more perspective on certain matters and freedom to be whoever she wants to be.
Wanna meet them? Please check out Menmar!
Sarah would play some sort of magical class, most likely a wizard. She'd pick something relatively safe and simple
Castiel would be a fighter or rogue. It'd be a hard decision because on one hand he wants to fight enemies with cool sword, but on the other hand being a sneaky rogue sounds fun.
Amanda would play a druid. They hang out with animals and turn into them too. That's all she needs.
Leon would be a bard. He doesn't care about the fighting but definitely doesn't mind bursting into song in the middle of a battle. Finally he can use all the song lyrics he hasn't found proper usage for yet.
If my main character were to play D&D, I would say this:
Ava - Fighter: She would like the idea of having an offensive weapon and a shield. She's not particular about being a virtuous character like a Paladin, but she wouldn't be an evil one. More like she would be Neutral-Good, or is it Lawful Neutral?
I love this!
For my mains it'd be:
Allura - Paladin taking the Blackguard route because honestly she's sick of the BS that comes with being a hero and wants to pretend she evil
Axis - Rouge so he can hide from BS or cause it
Flora - A bard because she's going to make a character that does not share her abandonment issues, and this way she can swoon all the pretty ladies
Gotta say though, never played D&D myself but that's about to change. My friend invited me to his long term campaign and I can't wait for it to start 
I actually made some drawings of my main characters in a dnd au.
Flare: She would definitely be a tiefling monk. Her fighting style is based on punching and kicking everything in sight, and the fact that she has fire powers mixes really well with the Ascendant Dragon path (even though I think it's still on the works). Also she would subclass as a rogue.
Shade: Despite his low charisma he would try to be a (not very effective) warlock. Thankfuly he's good enough with a sword but you can't really count on his spellcasting ability. He would subclass as a barbaria probably.
So I have actually played some of my characters in dnd
Rokuzo: Sorcerer and monk- not only does his fight with magic, but he back it up with his fists.
Ahikok: Sorcerer and fighter- She is a bit of a tank-y spellcaster.
Enossa: Artificer - because that is what she does already
Don't play but I know a lot of people who do and I know a few podcasts so here goes:
Agony: Rogue- when asked why she responded with "screw you" Makes fun of literally every character that gets introduced
Thesis: Wizard- acts like he knows the game better than anyone else playing but really has no idea what the hell he's doing
Duenna: Druid- Only agreed to play once and then won't shut up about what a waste of time the game is and how is "causes violence"
Motif: Bard:-Is chaotic and obnoxious and spends the whole game doing stupid things he thinks are funny
Sequel: Item- He's literally just an Item that Motif insistently carries around and it rarely does anything useful.
Ruby: DM- no comment.
Anselme would play Paladin - He's pretty much facking his devotion so he cannot choose any class with bad reputation
Sonia: Wizard, sure she has knowledge and knows how to spell. Also she does not put herself in danger, distance is her go to
Katia: Barbarian, she's 2m tall, she does the job
Philharmonie: Rogue, he likes any stealth thing and using is brain makes him good or barbarian, because he wants to be like Katia.
Symphonie: She's the DM lol She would have played as Ranger if she was not so ruly, I guess
Melodie: Bard or monk depending on the game. She's mostly social and pretty flexible.
Valère: Sorcerer, not going to fight willingly even as a character, he prefers thinking and helping
Just found an old sketch playing with that idea for characters of Rocky the Rock
Rocky the rock would be a knight, paladin or something that is ridiculously good at tanking. Rocky is always protecting others and he nevers begins a match, but is always ready to finish it.
Other players would consider him the team leader without second thought.
Kimura would attempt to multiclass to get the best of everything, but after realizing that leads him with an innefective build, he would play a sorcerer focused on offensive spells. A sorcerer specifically because he is impatient and doesn't plan too much, so the wizard preparation methods would be annoying for him, and not a warlock because he doesnt like relying on an outside source for his power, even if it is just a patron. He would get killed a lot because he would go to an unneccesary close range or for not realizing he is in the area of effect of his own spells.
Jenny would definitively play support: Her kind heart and strong teamwork spirit would lead her to fill the empty role. She may be a cleric or a druid. Prone to having summoning spells prepared because animals/creatures are cute.
Would try to use diplomacy even in non-sentient creatures like golems and skeletons. May ocasionally forget some of her abilities.
Also, she will always have raise dead (or reincarnation if she is a druid) in case someone (mostly Kimura) dies.
Medusa would play either a rogue or a bard. She would be really invested in roleplaying and taking the spotlight.
May take the feat leadership if it is allowed to have some henchmen at her service.
Finding Work:
Cherry: Palladin - Cherry has a noble heart, and she'd make a character that can embody her noble ideals without having to face the systemic challenges she deals.
Takir: Bard - Takir wouldn't be a flirty bard. He'd get very invested in the music aspect and storytelling. He likes to entertain and make jokes.
Arya: Bard - Arya would be the typical seduce-everyone type of bard. She'd have fun with it.
Glunk: Sorcerer - Glunk wants to cast fireball
Brun: Palladin - Brun wants to have a story about her being a noble knight that rescues the princess. She also wants to crush the princess between her thighs.
Ghal: Bear - Ghal would be the type to play as an actual bear.
Elra: Elra's the DM
The Shopkeeper
Arin: Druid - Arin would be a druid and spend most of the game polymorphed as a squirrel or something so they don't have to participate
Vea: Healer - Vea is a cinnamon bun and wants to take care of people
Gemini: Healer - Gemini doesn't understand why people keep encouraging her to be something other than what she already is
Wren: Rogue - Wren would be a rogue, not because he wants to be, but because Gemini made him play and she thought he'd make a very dashing rogue.
Brooders
Wendel: Necromancer - Wendel would play as a necromancer or dark sorceress, but he'd make a girl character because he thinks it'd be nice to try and it definitely isn't a sign of anything. 
Garson: Assassin - Garson would try very hard to be the edgy assassin type but wouldn't be able to commit to the evil alignment he chose.
Cecillia: Cecillia would be DM after everyone got tired of Elra manipulating them.
Ashleigh: Wasn't invited
This was a fun topic 
Bestia: Fighter, Barbarian, or druid. She likes fighting, and she would be interested in playing a nature-related class
Sharack: Death Knight - brooding and tragic, or paladin, in memory of her more heroic past self
Koth: Bard, would be the source of last minute solutions
Lana: would be the GM, and would likely play a support character
Styrak: Likely a caster class
V: Monk or bard, they will likely build something fun and a bit more socially oriented
13 days later
I'm still early on at the moment, but I'll include a few important characters that'll appear soon. All of them are fighters/magic-users anyway so this kind of feels like cheating...
Kovreil: Barbarian, almost exclusively for the ability to rage -- he has a reputation for being an incredibly aggressive fighter so this is a straight shoot
Modrian: Monk or Rogue, he's the one I'm most divided about because his actual fighting/magic style is sneaky and tactical like a rogue, but he's also an important peacekeeper so I feel like a monk would suit his personality more
Sengad: Paladin, he's an absolute tank but also the human equivalent of a bear hug and very principles-driven
Corin: Wizard, generally something scholarly that would let him help others
Erik: Fighter bc he's good with a sword and leading people.
Luis: A paladin because later in the story he fights for his gods and will.
Sara: Rogue, because she's sneaky and has many stealth/scouting missions.
Tonya: Life Cleric because she heals everyone and keeps them alive/safe
That's as much I could think of so far...
A great topic
My main character would play a Rogue. Just because it is the way she lives her life - loving to steal stuff, just for fun and of course for the money.
Funny enough my character actually came from times where some friends and I came together and tried (the emphasis on trying ^^) to play some RPGs. She was planned as a throwaway Rogue character, but I liked her so much that over time (and after we disbanded our group) she became
Oh my gosh, I love this concept. Also its funny cause I do play a couple of my characters in actual DnD campaigns!
Perry: This is the character I main in one of my campaigns, he's a rogue/ranger in that. But I feel like he'd lean more towards playing a bard, just because bards have a reputation of being seductive and he'd LIVE for that
Ryn: Wizards are the nerds of DnD mages, and Ryn would DEFINITELY identify with that. But in the end, Ryn would probably be the DM for the group
Amethyst: Her pacifist personality would stay strong even in a "fictional" scenario, so she'd probably choose a cleric. A very lawfully good one at that
Qing: Oh man, this one's a little hard...She'd definitely be confused by the point of DnD. But probably after a lot of insistence, she'd go with a fighter since it's a pretty standard class
James: Being the one person in the group who can't actually use magic, he'd probably be a warlock because hey who doesn't like to get into deep trouble with the gods in exchange for being able to conjure fire with your fingers?
Harrison: Oh this is so easy, he'd choose artificer in a heartbeat, no argument there!
Pablo: Like Qing, he'd be very confused on why DnD is a thing. He'd probably pick druid because the concept of turning into an animal sounds kinda neat
It's funny you say that the reality of the comic highkey uses D&D as a foundation, I also sometimes roll dice as apart of the writing process (and to get numbers in there)
Anywho...
Lanny (Chosen one): Vengeance Paladin (5th level), Lucky Feat, to reflect inevitability and his chosen one esk prophecy. Would constantly have foresight on him :U
Mira: Eldritch Knight (5th level), with some kind of fire-themed booming blade that triggers on forced movement as well (she can never trigger forced movement herself), and a general explosion attack that deals far less damage but the effect is immediate.
Sally (The Dark Lord): Great Old One Warlock (because it's the closest match thematically), Also with some kind of foresight spell.
Koah (TDL's right-hand man): Paladin, but I won't reveal much more until later pages xD. he is not an oathbreaker, even though he DID break a previous one for the sake of literally the dark lord. Completely different oath.
Koah Spoilers
he is canonically a redemption paladin, Since the point of his character is that he sees good in everyone, even Sally who is the great evil in the world. One is a pacifist, the other is death.
His greatsword vessel has the ability to break weapons and armor, without doing a single point of damage to his enemies. And Koah has a lot of negation/counterspells to deal with spellcasters, as opposed to fizzling the spells, he weakens the spell so hard that it turns into flowers/feathers instead of something actually harmful.
Shadowy rogue character: Is a rogue (some kind of saboteur rogue archetype, about bomb planting.) has an ability that can create an explosion that forcefully moves the target, great synergy with Mira's other explosion move.
The Hemomancers: Oddly, some might be wizards, but the practice could also fit into being monks. This was realized later on in the writing process of Doomed One(s) since their practice is all about precise control over their own body (and others if you're well trained enough). Their fighting style is very acrobatic and weakspot focused which is big monk themed. The hemomancer who lacks eyes on their bird mask would be some kind of mercy monk/wizard of some sort.
yeet