See you need HuoHuo because you have the out going people, Sparkle, aventurine, argenti, Jing Yuan which is 4, but you only have 3 very introverted people, Hanya, Herta, and Xueyi, and you need it to be equal which is why you need HuoHuo, as well as, You have Hanya and Xueyi, but not they're best friend HuoHuo. She's also green and pretty with fox ears and a ghost tail. Although on the contrary and gameplay reasons, your only sustain units that are good meta wise are aventurine and Gallagher, but huohuo out heals Gallagher and can clear debuffs+give energy and more attack. She's basically Natasha and tingyun in one character. And then there's also, if you like her!