Yiyi Xu is a professor and a scientist at Alltale Management Facility and colleagues of Tsunehisa Senko and Katagaki Naomi. She is a serious and hardworking person and friendly towards her fellow workers. She loves to follow rules although Professor Senko's work habit rubs her eventually and in certainties follows his example. Just like when their group decided to throw a barbecue party at the facility hall at the time when the security guards are not roving their area. She has a habit of intruding someone's room and to make a 360 degree cleaning. When she gets worried, Yiyi frequently speaks on her native tongue.