So, I'm currently trying to create a campaign in a sci-fi setting in 5e. It's going to be relatively soft sci-fi, with a few magic-like elements such as psionics and something similar to the force. However, such things will be extremely rare, and thought to be nonexistent by most people. What I'm not looking for is old men dressed in sparkly nightgowns throwing magical fireballs at madduce spaceships. I can't just eliminate all magical classes though, as such things are central to D&D 5e. Instead, I need to find some way to reskin them. Now, before you go typing your response, let me make this clear. I am NOT looking for answers stating "D&D 5e is too magical oriented, so you should do it in this system." I know this. However, I've found several excellent sci-fi supplements for 5e, and I would like to use them. Also, more importantly, I feel comfortable with 5e. The only other system I've ever played is 1e, so I'm definitely not going to try and DM using a system I've never even played. All I'm looking for is suggestions for how to reskin different types of magic using classes for a sci-fi setting. Thanks in advance to anyone who might respond to this.

Nanites. Magic is just control over alien nanites.

Thanks, I hadn't thought of that!

Paladins are injected with nanites, which empower their attacks and let them heal/buff others. When they take their oath at 3rd level, the words uttered act like a sort of passcode, unlocking more of the nanites' power.

Some sorcerers would get their powers after accidentally getting a bunch of nanites in their blood.

Wizards/Eldritch knights/Arcane Tricksters are experts in the field of nanites, their spellbooks being specialized nanite controllers, which have different series of commands which can be issued to the nanites in order to accomplish amazing feats.

Bards control nanites with music? Seems both improbable and inefficient.

Clerics, Druids, Warlocks, and possibly bards don't work well with nanites.

This reminds me of Jack Chalker's Charon: A Dragon at the Gate.

Flip it on its head: the nanites are not solely in individuals. Nanites are free and permeate the world, as well as people.

Magic then becomes the ability to mentally communicate with your nanites, and to prompt your nanites to communicate/control nanites in the world at large.

Knowledge based spell casters are akin to programmers.

Sorcerers are akin to Hackers: they're very naturally talented at manipulating the nanite networks, but may not fully understand the theory behind it ( although some Hackers/Security Researchers are very knowledgeable about theory IRL ).

Since a person with nanites in their system would be living symbiotically with them, then it stands to reason that changes in their emotional/mental states would be reflected in the state of their nanite symbiotes. Bards use music/theater/poetry to put their targets' minds - and thus their nanite symbiote networks - in a receptive state before directly manipulating them  more directly in a manner similar to what Sorcerers do ( kind of like the social engineering side of hacking ).

Clerics ( and Warlocks ) enter into relationships/contracts with sentient programs living in the global network of nano-machines ( the nanisphere? ).

Paladins adapt & maintain themselves in a particular mental/psychological state ( their oath ) which allows them to interface more fully and more consistently with their own nanite symbiotes, and to some extent, those of the beings around them.

Druids are experts at understanding the functions of local symbiotic nanite networks inside living beings, how they interact with their biological host, and have the ability to cause resonances between networks, or even impose one network pattern onto another ( wildshape, polymorph, etc. ).

Does that work better? :)

I like that. However, it may pose a bit of a problem, as new, undiscovered planets as well as much of space would be utterly without nanites, and therefore magic. This would put any casters at a large disadvantage during any exploration mission. Perhaps then a popular sold item would be large canisters of nanites, which could be released into an area, therefore enmagicing it. I'd need to come up with some reason for why nanites are everywhere, but that should be easy enough. Perhaps some small company came up with them, and they quickly spread all over the known universe, until the matter quickly went from whether you had nanites, to whether you could control them.

Now we're exploring space and other planets? Man - you keep moving the goal post ;D

I could see Wizards performing rituals which channel their own internal nanites into the environment to replicate and infect the local environment: Create Magic anyone?! :D

I don't know if you'd need to "enmagic" an entire biosphere; you could definitely carry reserves of nanites within you, even in areas which are not infected by nanites. If you did this, it would mean that different schools/types of magic would work differently based on the presence/local-level of nanites. I can see there being an edge to evocation magic over things like enchantment. In the former case, I would just have to get a nanite projectile in a position to release energy ( I'm think fireball or magic missile ). In the latter case you'd definitely need to infect your target with nanites to affect or transform them. Paladins might retain their personal abilities, while abilities like divine smite might depend on whether or not the target is infected with nanites. Fortunately, undead pretty much have to be nanite animated.

A partially infected biosphere would be interesting. Magic would work ( or not ) to varying degrees across the biosphere, as the infection spreads.

It would explain why different realms have different "gods" however - different AI programs evolve out of the nanisphere, in physically disjoint nanite ecosystems.

It definitely would give magic, and the whole fantasy aspect, a different and unique twist.

Dropships just unleash a nanite payload as part of landing protocols to help the landing team and the ship interact with the local terrain. It was a thing protested early on by "first contact" protesters, but the galactic authority has deemed it acceptable and thus the bots have spread to countless worlds.

" ... it was this practice of indiscriminately infecting alien world with utility fog which ultimately lead to what would later be called the Replicator War. In 2752 DR, an automated seedship from the Faerûnic Collective infected the Cruuqned homeworld. In retaliation for this perceived aggressive act, the Cruuqned launched a series of impactor attacks into the Sea of Fallen Stars. The subsequent tsunami wiped out the cities of Westgate, Selgaunt, Saerloon, and heavily damaged Suzail and Marsember. The conflict lasted between 2752 to 2773 DR, and was responsible for the rise of the .... "

Perhaps there could also be a certain religious sect which denounced the use of nanotechnology(sort of like the tonists in Scyth, if any of you have read it), and set up a constant emp forcefield thing around their worlds. Any technology within would function, but any brought in would immediately become inert unless they opened a hole in the barrier to let it through. Any ship that passed through would be searched throughly, and scanned for any of the distinct waves which nanites use to communicate with each other.

Also I'm definitely including the replicator war in my campaign(or at least mentions of it).

I know I am WAY late to punch, but a common theme in nanotechnology is self replication by consumption of the necessary metals (an example is the book: God AI). So just the mere presence of someone with the nanites would spread it to any planet with metal. So think of the nanites like viruses, humans and infected aliens as parasite carriers (since we are kind of parasites to our planet), and planets as the infected.

This way, the company who made the nanites would not have to mass produce them but more accidentally release them like the creation of killer bees. So most society has except the nanites, but many people and MANY extraterrestrials see it as a planet disease that they need to find a cure for.