Qin Shi Ming Yue: Ye Jin Tianming

In the second season, Emperor Qin sends Quicksand to destroy Machinery City, the home of the Mohist School. At the same time, Duanmu Rong sends the three kids, Tianming, Shao Yu, and Gao Yu, into the forbidden grounds of the Mohist School, a place where nobody could enter without permission. (Source: AniDB)