True Love is listed as either a minor general virtue, or as a major story flaw.
What happens if two characters have True Love between them, and one gets transformed somehow, either to a magical or faerie being. Does True Love survive the transformation ?
"The Princess Bride" suggests yes. RoPM says a Divine supernatural virtue is lost.
True Love/Friendship is not a divine virtue or flaw as far as I am aware. It can be gained via magic with the familiar bond. In my estimation it’s more like an Essential Trait so I feel it would have no problem surviving Magical transformation.
As it needs to be two way I do feel like it would not survive a faerie transformation unless some piece of a particular faeries role(s) can truly be immutable.
Magical, I see no problem. As @dc444 mentions it already exists between magi and their familiars, who are magical beings.
For faeries I am more sceptical, as I dont think faeries are capable of any true emotion which would exclude true love. Faeries no doubt love True love, because it gives rise to a great number of powerful stories for them to feed on, but I dont think they are capable of feeling love themselves.
The familiar argument works both ways. I think Faeries can maintain True bonds because, Serf's Parma, Merinita magi can have Faerie familiars and even turn themselves into Faeries via their Mystery Path, without losing their familiar bond in the process?
Also, while this doesn't strictly answer your question, I think that if a transformation would break a True connection, the rules of said True connection would prevent the transformation from occurring. That might be me reading True Love/Friend too generously, though.
the bond of a faerie familiar however is impermanent, so it may simply give it a role of True friendship rather than actual true friendship. That being said I think if a faerie has a bond of true friendship with a human they will be loathe to give that up due to the potential for vitality, and it will be true on the human side. as such I would think the possibility of it ending with a faerie would be similar to the possibility fo death with a human, and should be allowed as equivalent of not exactly the same.
Can the Transformed Merenita create or maintain a familiar bond with a Magic creature? The Mystery Virtue might forbid it, I don't presently have a copy of the book since my computer broke, but if they can, those don't decay. In which case you can either conclude that faeries in general can have True bonds, or (on an only tangentially related matter of dispute), if they can't because True feelings come from the Limit of the Soul, that magi don't lose their human souls when they become immortal beings of Might. Which would sure be a relief to several mystery cults' highest members.
I believe they can form a familiar bond with a magical creature, but in the HOH:MC it indicates that if they ecome faerie that even bonds with magical creatures will decay due to the faerie nature of the magus.
Perhaps "transformed" was the incorrect word. I was intending a mundane human transmogrified into a creature with supernatural Might. Ascension to the Hall of Heroes, Faerie Becoming, or something else - say a Norse witch who undergoes (perhaps not voluntarily) a Muspelhiem ritual and is transformed into a Troll-sorceress foot soldier preparing for Ragnorak.
Simple shapeshifting, as per the Norwegian fairy tale, stills means that the Essential Nature of both of the True Love pair are still mundane human.
So True Love is both lovers' Essential Nature, and then one gets their Essential Nature changed, right? Looks like irresistible force meeting impenetrable barrier - so the SG makes up an explanation of what happens why.
The story gets most interesting, if the change works - but not completely or for ever: think Bjornaer transformed and struggling with Heartbeast Ability to reverse it. Then one lover chases the other to save him, followed by a dozen troubadours recording her troubles ...
A faerie blooded Dhampir becomes a faerie vampire after death. Does True Love survive death?
Possibly other transmogrifications of mundane mortal to creature with supernatural Might could also be said to involve the death of the mundane mortal. Could this be a natural barrier to the continuence of True Love?