I name it the Reluctant Wizard AU
The rumors of Varian being a wizard are true. Alchemy is still his ACTUAL passion but thanks to his awful luck he becomes a mage on the side to deal with the magical shenanigans that occur without fail. Since I am a sucker for Moon!Varian that is a thing here too. Things go down the same in the Dark Kingdom and Quirin gets blasted by the Moonstone.
Here in this AU the Moonstone and Sundrop are sentient. They both prefer to take the form of women and were worshipped as goddesses. Moonstone is named Lunafreya. I have tentatively named the Sundrop Aurora. All went well until Zhan Tiri hijacked the stone and places of worship meant for the moon. She threatened and killed until people considered her the moon goddess and Lunafreya got shoved to the side.
Cue to more or less present: Lunafreya got curious of the baby with her powers. She visited Varian and grew attached. Lunafreya declares him her"Little Moonbeam". She then proceeds to sing Varian lullabies and tells him stories.
Quirin and Ulla FREAKED when they noticed the ghostly lady hanging around their son. They went NOPE and packed their bags to Corona. After saying goodbye of course. Let Varian have family in the Dark Kingdom he exchanges letters with and visits on occassion. Awesome Sword Aunt and Feral Tree Uncle teach him to fight and use weapons cause they be like that. Quirin is a silent Despair in the back but agrees that his son knowing how to defend himself is a good thing.
Ulla notices the Moon Powers and goes looking for the Eternal Library for answers with Donella. It goes as well as predicted. We now have the V&7k plot waiting in the wings.Meanwhile Lunafreya can't leave the Dark Kingdom but since DREAMS are part of her domain she can still contact Varian. After earning Varian's trust she teaches him Magic & Alchemy. Lunafreya decides not to teach him about his moon powers until Varian is older and in the Dark Kingdom to supervise better. Varian calls Lunafreya as Mother while Ulla is called Mom.
Varian decides that people knowing about his magical powers and connection to the moon is too dangerous so he tries to hide it. Keyword being: Try. It is literally the worst kept secret cause Varian is a human disaster. He isn't discovered because Quirin is vibing in denial and busy with work. The villagers chalk up the explosions to Alchemy Experiments. Varian is Clark Kent-ing through life so hard.
When Rapunzel and co. arrive he is an internal scream. He still helps though cause he's sweet like that. Varian mostly sticks to Alchemy but if things get bad enough he will use his powers. Varian then proceeds to frantically bluff his magic away as regular tricks while everyone side-eyes him. Don't get them wrong, they like the kid. They just conclude its actual magic but can't prove it. Rapunzel subconciously senses his connection to the moon and goes "Guess I have a little bro now".
Queen for a day happens but Varian doesn't have a villain arc cause Lunafreya talks sense into him more or less. He's mad at Raps and the king for canon reasons though. Varian is just a constant state of tranquil fury and gets noticeably ruthless. Thanks to King Frederick's poor life choices he decides to leave for the Dark Kingdom. He is definitely not coming back until he can find a way to free his Dad and King Freddy stops drinking dumb bitch juice. There is much learning of lessons and character growth for the cast.