The scar on his heart

"Xinyi? Are you talking about the one who was in the cradle when I went to play with you?" Zhai Tianyu asked as he popped his head out of the wooden screen behind which he was changing clothes. He would not have done it but it was in fact too shocking for him to stay calm. He was not old but he was definitely much older than Ji Xinyi. "Isn't she like twelve or thirteen?" 

She was yet to turn fifteen and he was already going to be twenty years old very soon.

"Yes and Yes she is thirteen," Ji Yu replied causing Zhai Tianyu to crash on the ground. Almost. He changed his clothes and stepped out of the wooden divider before walking to his bed and saying, "Why did you not stop her? Xinyi is too young to be thrown in the mess of harem." More importantly, it would be weird for him to share a bed chamber with a thirteen-year-old girl.