FrogReaver
The most respectful and polite poster ever
How about something like:
Nystul Aura Swap (level 2)
Casting Time: Action
Duration: Instant
Range: Touch
When you touch a willing target, you may transfer any and all spells up to 2nd level affecting you that do not have a duration of Instantaneous or Permanent or are under the active concentration of someone else. Any spell without concentration or that you are concentrating on may be passed on, including passing the concentration requirement to the target. They assume full control over those spells as if they had cast them.
You may cast this spell using a higher level slot. This will allow you to pass spells of levels up to the slot used.
That may fit the narrative better. My concern is doing things outside combat where action economy isn't as a great a cost like passing an 8 hour Hex of Hunter's Mark to another person. But even there it's not too bad.
Nope. The fighter that doesn't use any magic at all. How the heck does he know how to concentrate on any kind of magic in the first place? If it was restricted to passing the concentration spell to other spell casters it would at least make sense narratively. But the guy that doesn't do magic doesn't suddenly start knowing how to concentrate on magic enough to keep it up and running.
So the spell would actually need to be doing 2 things.
1. Allowing the spell to be transferred
2. Giving the magicless fighter the information needed to concentrate on a magic spell.
Seeing that the 2nd part isn't mentioned as being done anywhere in the spell is the disconnect. Also if magic can allow non-magic users to concentrate on spells then can't magic allow non-magic users to start casting spells too? Is that really a road we want to go down?