Taiji (Yin and Yang) the meaning of opposites being balanced. In good there is always evil, and in evil there is always good. 

We all wished sometimes that superpowers were real either for entertaniment or to feel the glory of a city hero. Sometimes EXO wished their superpowers were real. Sometimes, Yixing wished his healing power was real. Only so he could stop seeing his memebers cry, to mend their hearts. Sometimes, Tao wished the same. That way he could go back in time to prevent from all this chaos happening, or to completely stop time itself because time is limited, especially EXO's.