The 'Onii-chan' meme stems from a common honorific used in Japanese anime to address an older brother. While it has been a staple of the medium for decades, it became a widespread internet meme through viral sound clips and reaction images featuring characters from shows like Eromanga Sensei and various 'imouto' themed series. It is often used to parody the 'cute and innocent' or 'obsessive and clingy' sister archetypes found in otaku culture. Today, creators use the template to react to various scenarios, often contrasting the high-pitched, adorable delivery of the phrase with absurd or dark context to create a humorous and often ironic juxtaposition.