DMMD is the common shorthand for Dramatical Murder, a Japanese visual novel that later received an anime adaptation, and this clip comes from its fan soundboard culture. The spoken line is a polite Japanese morning greeting, ohayo gozaimasu, addressed to Master, a form of address that fits the series' character relationships and roleplay appeal. Fans have shared short voice lines like this one on soundboards and in edits for years, and it remains popular because it is instantly recognisable, easy to place at the start of a video, and carries a warm, distinctly anime feel.