Tian Cheng should let Xuan Xuan hold onto the meteorite sword as well, so that the sword would suck crimson demon virus energy out of her, alleviating the symptoms of the infection. She hasn't got an internal connection with the sword, but does that really matter? A person can have a loyal customer card of a certain gas station chain, for discounts, but it doesn't mean the person couldn't fill up at any random petrol station.