Princess Raia is a character that appeared in the real Sir Gallant's comic books and videos about his adventures. She is a princess from the same planet as Sir Gallant himself, whom he protected from the monsters plaquing the galaxy by sending her far away from himself long ago. It is somewhat hinted that Raia was Sir Gallant's love interest.
Interestingly, the man who claims to be Sir Gallant also claims that he did the same thing for Princess Raia, just like the real Sir Gallant did. But this is partly because he's just been reading too many comic books and watching too many videos about him. He even takes on the same name and heroism as him too. He even mistakes Mabel, the fortune teller, for Princess Raia. When he seemingly dies at the hands of his archenemy, Windwhipper, Mabel pretends to be Princess Raia, slapping him back to his senses and telling him not to lose faith in himself as there are other planets that needed his protecting.
Princess Raia is a baby Cappy, and looks just like Mabel. Because the two look so similar, Sir Gallant actually confuses the two for each other. Raia only makes a few small appearances in the episode, namely in Sir Gallant's comics and his "memories". In both scenes, she appears adorned with lavish jewelry and wrapped tightly in a pink blanket for warmth and protection.
The differences between Mabel and her include, not only their size and age, but also (to an extent) what they wear. Raia only wears a golden headress, whereas Mabel has bracelets, earings, and fancier headgarb.