Cremene is the main antagonist of the 38th chapter of Miss Kobayashi's Dragon Maid entitled Kobayashi and Iruru.
Cremene is a mysterious dragon hailing from the Harmony Faction. Much like the other Harmony Dragons, Cremene despises the Chaos Dragons, so much so, he embarked on a genocidal crusade to erradicate the Chaos faction. Cremene makes his introduction by following Iruru to Earth. When Iruru was by herself, Cremene proceeds to violently attack her despite her being defenseless. Before he could finish the job, Kobayashi intervenes, and chastises him for beating on a child. Unlike the other Harmony Dragons who - while disliking humans respect the laws prohibiting them from harming them - Cremene bats Kobayashi out of the way, and attempts to murder both of them.
Cremene takes the time to gloat about how "lucky" he was to have found Iruru, only to come face to face with an enraged Tohru. Tohru proceeds to heavily beat him for nearly killing Kobayashi, and she ultimately wipes his memories. She explains that if she were to have murdered him, that would've inspired other Harmony Dragons to invade Earth. Apparently, Cremene also knew Elma (a fellow Harmony Dragon), if preferring to her as "Lady Elma" wasn't any indication.