The line comes from Yasuna Oribe, the cheerful schoolgirl at the centre of the anime Kill Me Baby, who delivers the Spanish greeting buenos días in a bright, friendly voice. Shared online as a short standalone clip, it caught on because it is instantly recognisable, easy to understand even without knowing the series, and works as a warm hello in any language context. Fans now reuse it for morning posts, greetings and lighthearted edits, keeping the moment alive long after the original scene.