Meroune Lorelei—Mero to most—is a mermaid who uses a wheelchair. She's technically the fifth girl to move in with Kimihito, though officially counted as the fourth, since Suu got there first but never actually registered.
What people notice about Mero right away is her warmth. Centaurea has mentioned picking up distinctly royal vibes from her, and that tracks with how she carries herself.
Her whole thing with romance comes from childhood. She became obsessed with Hans Christian Andersen's "The Little Mermaid"—specifically the tragic elements—and decided she wanted to live out that story herself. Like, actually live it. She's drawn to the idea of a doomed love and even accepts the possibility of dissolving into sea foam at the end. What matters to her is being a lover, not a bride. It's a weirdly specific fixation, but it shapes pretty much everything about how she approaches relationships.
Content compiled by AnimeList.moe from publicly available sources.