许你半夏倾城
[xŭ nĭ bàn xià qīng chéng]
It comes from the context of romance or literature in Chinese culture. Half summer ('半夏') can indicate half-life or fleeting beauty of youth. '倾城' originally means charming enough to make a whole city turn around and gaze, symbolizes extraordinary beautiful, so the entire phrase conveys a pledge of giving someone an unforgettable memory as beautiful as if it was enough to enchant a whole city.