Busted! Darklord.

In an attempt for survival, Yu Renjie, the son of the demon lord, was ordered to enter Hero's Academy which only recruits distinguished and upright disciples. The goal is to obtain a Hero's Certificate which can bring legitimacy to the demon clan. This is extremely dangerous. Once the identity of a demon cultist is exposed, countless righteous knights will kill them on the spot. But on the first day of school, Yu Renjie was shocked to find out that his personal information had been leaked. In ...

Adaptation of Zhushui Guai Xiang's (注水怪象) Chinese webtoon of the same title.