Sister Rong is one of the six elders of the Mohist School and probably their best fighter with needles—she's also a skilled medic. Her old teacher made her swear never to treat swordsmen or anyone using martial arts for selfish reasons, which becomes a real problem when she meets Ge Nie, an injured swordsman who was actually defending her friends. Tianming eventually convinces her to break that vow.
With Yue-er, she's like a real older sister despite not being blood-related, and Yue-er clearly picked up her underlying kindness. It's one of those genuine relationships that defines her character.
The messier part of her story: she and Ge Nie fall for each other (he loves her too, though it takes a while to confirm), and when Baifeng attacks, Rong takes the hit meant for him. She never wakes up after that in season three.
Content compiled by AnimeList.moe from publicly available sources.
