E-Rank? No, I'm SSS-Rank Dragon God

The son of an E-rank corpse cleaner, to save his mother who had been cut off from medication, forced his way into a selection contest controlled by a wealthy clan, only to discover that an SSS Dragon God was sealed within him, and all his enemies' abilities were fakes created by serum—ultimately he staged a comeback and made the young master who had crushed his potion pay the price.