Undyne

Undyne is an main character the player meets in Waterfall, first appearing as an imposing titan in a suirt of menacing black and white armor, she later reaveals that she is actually a slim fish-woman with blue scaley skin, a black eyepatch over one eye, and long bright red hair growing into a natural ponytail shape

She overzelously believe in Asgor's plan to capture the humans to break the barrier and start a war and relentelessly chases the player untill she is defeated or saved in hotland, despite her hotheaded nature and agressive tendancies she is actually a kind person who dislikes needless killing.

She attacks with magical javelines made of either water or magic energy, reprisented in battle as arrow-shaped bullets

She has romantic interest in Alphys, and has a warped perception of human history and culture due to her only exposure to human media being anime

fans have noticed that her behavior, apperance, and her clothing out of her armor bare a strong resembalnce to Vriska Serket from Homestuck, which makes sence since Toby had worked on making music for homestuck previously and is a fan of the comic