i may sound crazy for this but. skizz-lizzie siblings. no, jimmy and lizzie aren't siblings (not by blood at least), jimmy is pearl and grian's brother. but... ANYWAYS. I don't know where this idea came from but imo they're a very underrated duo so... ya :3
Ender/Fae genetics, Skizz got more of the first half of that and Lizz(ie) got more of the second. (And then Skizz died and came back able to shapeshift just like his sister could already do, but that's besides the point)
and of course if we play into one of my very favorite headcanons. imagine. the both of them growing up in the Seelie court (their land was much kinder to mortals, given that their ruler had fallen in love with one). skizz never quite fitting with the magical aspects, never understanding the thrill everyone else seemed to get from the Hunt. never quite perfecting the laws they have to abide by. meanwhile lizzie shaping up to be the perfect next ruler of the court, and yet still finding time for her little brother. helping him realize things about himself (*winks in transmasc*) even though she doesn't quite understand it (after all, the faeries are magical creatures, borne of it, exactly how they want to be in every way).
then one day skizz makes a friend on the edge of the forest's border! a mortal, half-demon and half-rock giant, who tries to kill him at first sight (before realizing that wait, nope, that's one of the fae, BAD IDEA). They get over it and become Besties. and skizz gives up some of that immortality, that magic, in order to well and truly live. mortality sounds fun! Lizzie, of course, sends him off with a smile and a reminder of her love in the form of some (non-magic-imbued) pastries. Skizz comes back two weeks later with some new friends in tow, stays a few days, leaves, comes back again. It continues.
And then one day, he brings another friend with him: a human, some kind of mage, with a streak of green in his hair. and gods, if lizzie isn't (internally) struck dumb at the sight of him!
At least she's subtle, though. The cute human is so obvious, turning into a blushing mess whenever he tries to talk to her, and honestly it's a little embarrassing at this point!
...doesn't change the fact that, a few years later, skizz comes back to the court for a very special occasion. Seems this lineage has a bad habit of falling for mortals, one way or another!