Merfolk can be a magical people, and in particular, a vengeful queen of a deep sea Mer colony thought to create the perfect princess for her kingdom through arcane means. Naturally undergoing many mishaps, the eventual offspring Corallia grew at incredible rates beyond what could be reasonably sustained, and eventually was banished. On her own, it didn't become long until she had bumped heads into a beach. Fortunately having been taught to speak properly, if still a little inexperienced, she managed to actually make contact with some of the normal sized beings on the surface, but is early in her days of social interaction. Easily bored, it was a lovely diversion to meet the rare person that didn't bolt or shriek at the sight of her. The sight of those shining cities teasing her in the distance makes her desperately long for a day in which she could walk herself and get legs of her own. For now, she's constricted to the seas, shores, and larger rivers. Learning about the strange things that people can do and make is one thing she has struggled with, however. ( Depends on if it's a fantasy, modern, or sci-fi setting! )

She divides humans and land-dwellers into two classes. First there are the screamers, who pierce her sensitive eardrums in terror whenever she surfaces. The sheer headache she can get from just showing up on a beach can be awful. The lack of reasoning or common sense in mind, Corallia sees them as less than sapient, and the so called 'screamers' are little more than delicious squirmy candy to her. It's not easy to listen to noises coming from her sloshy tum though, so even if she can very easily bring things up from her depths, it is a rarity for strangers to get so lucky. Given that she can breathe in and above water, being found or rescued is equally unlikely. At least her stomach is immune to water pressure, making her an incredibly potent submarine for exploring deep underwater treasure troves and caves if someone is willing to take the risk. However, as a social being, with little if any creatures her own size, she loves to spend time around the 'talkers', or land dwellers that know their way around a conversation. A cheery giantess mermaid might be intimidating, but she has a soft, bubbly personality that seems out of place for a majestic, one of a kind titaness such as her!

TLDR: Giantess mermaid!