Amyeong

Amyeong, aka "Dark" is an international criminal infamously known for hunting global rankers. He has illegally entered South Korea along with Dran, in task of killing Kayden.

[Spoiler] Based on a flashback it seems that Kayden and Amyeong have met before and are acquainted. It is stated that although Kayden does not recognize Amyeong as his disciple, Amyeong nonetheless considers himself to be one, which slightly hints at their past interactions and Amyeong's respect for Kayden as the strongest awakener. [/Spoiler]

(Source: Eleceed Wiki)