Kodachi with her "darling Ranma".
This is a page describing the relationship between Kodachi Kuno and Ranma Saotome.
Kodachi's desire for Ranma Saotome is perhaps the most blatantly one-sided romance in the canon of Ranma ½. In fact, in the manga, she herself does not seem to truly be interested in him except as a plaything, violently stalking him and attacking him for her own amusement. In the anime, she seems more sincerely interested in him and, it is implied, is more of a lonely girl who doesn't really know how to interact with others due to her background and family. In this canon, she has performed such feats as coming to Ranma's aid with food and money after hearing that the Tendo household is going through financial difficulties, declaring and showing her willingness to buy Ranma a dojo of his own (or anything else he may desire), and taking in Ranma and Genma both and showering them with comfort after they leave the Tendo household due to an argument between Genma and Soun.
In both canons, Ranma displays no reciprocation for Kodachi's feelings, in fact coming off as rather cold when taken under her roof in the aforementioned anime episode, and the fact that Kodachi is ignorant of Ranma's transformation and considers his female form a rival for his affections, treating her as an enemy, makes things worse.
Kodachi fell head over heels for Ranma after he rescued her from falling off of the Tendo roof, having accidentally knocked her out cold while chasing P-chan, and her thoughts and words imply she fell for him so hard because he was the first good-looking boy to act so nicely to her. Even though all he did was catch her before she hit the ground and sound genuinely sympathetic when asking if she was alright after coming to.