Ohayou is the casual Japanese way to say good morning, shortened from the more polite ohayou gozaimasu. In anime, school and slice of life scenes use it constantly as characters arrive, wake up, or meet friends, so international fans learned it as one of the first Japanese phrases they recognise. Short clipped versions spread online alongside other anime voice lines like Tuturu and Onii-chan, where the greeting works on its own without dialogue. It stays popular because it signals a fresh start and a friendly tone in under two seconds.