Some groups take ages to decide what their fans' name with be, others decide it really quickly or even before they debut. In other cases, they wait to decide until the fan/group relationship can develop a bit. Either way, a fan name is a big part of your interactions!
And TWICE decided on their fanclub name!
"We'll work hard so that you can look at us once, and fall in love with us TWICE."
You might think it's a little funny, but the reason they chose it is because they like the idea of saying "Once and Twice." They want fans to know that for everything fans give them once, they'll try to return TWICE as strongly.