
Actually you see Hyo Un calling Taehyuk *Sir* which makes english speakers or those who understand english like why Hyo Un is calling Taehyuk *sir* everytime...but he is not using the usual sir here, he is using a veryy interesting korean word
Nari (나리) or alternatively, naeuri (나으리), was used by commoners in the Joseon dynasty to address Noble people or lords...
As i have seen fair amount of korean historical drama i can hear Hyo Un calling Taehyuk "Nari" not Sir which feels very similar to when they replace Hyung with Brother
I hope you get it..so it's not a nick name but more like a way of addressing
I love Taehee for helping this himbo dragon to get his perfect proposal to his love his Nari
But what to do Nari is superrr pissed( ̄∇ ̄")