Originating from a 2001 adult video of the same name, A Midsummer Night's Lewd Dream (Manatsu no Yo no Inmu) evolved into one of the most significant and long-lasting subcultures on the Japanese video-sharing site Niconico Douga. Known as 'Inmu,' this phenomenon revolves around the character Yajuu Senpai (Beast Senpai) and a specialized vocabulary called 'Inmu-go.' While its origins are niche, the meme's usage has transcended its source material, becoming a medium for complex video editing, MADs, and abstract humor. Today, it remains a staple of Japanese internet culture, frequently appearing in parodies, urban legends, and even mainstream media references where the original context is often sanitized into absurd humor.