Arial was a presumably gnome girl. At some point in the past, Andrew and Ferdinand had already tried to get her to marry them, but when she refused, they remained good friends. Her father cursed her so she would forever sleep in the Cloud Castle until someone kissed her. Garth was madly in love with Arial and set about on his quest to save her from the curse. Once he finally did, Arial rejected him, not believing him to be her true love, causing Garth to fall into a deep depression, so much so that the idea of him and all of his newly gained friends dying in a castle collapse didn't phase him.
Garth did eventually used his Gnome magic to save them by creating a pool of mud underneath the collapsing, falling castle. Afterwords, Arial agreed to give him a chance.