What does Onii-Chan mean? I watched Himouto!Umaru-Chan and Umaru calls her brother Onii-Chan. Since Chan is a suffix after female names I was confused. At first I thought that it meant big brother, but I turned on a dubbed version and it still said Onni-Chan. So what does it mean?
You were actually right, Onii-chan means pretty much the same as Onii-san as in older brother. The difference is the former is informal or &quot;cuter&quot;, while the latter is more formal, as &quot;-chan&quot; is an informal honorific, while &quot;-san&quot; is a formal one.
According to this short Japanese honorifics lesson:

–chan
This is an endearing female honorific. While it’s most commonly used for children, it’s also used fairly widely among family and friends