Yoo In Na revealed her nickname for IU.

On December 13ths episode of KBS 2TV 'Win Win' IU special, Yoo In Na appeared as the hidden guest, confessing that IU has a mental age that reaches way beyond her 19 years of life.

Yoo In Na stated "When people say I don't think IU is a 19 year old, she could be 30" I say "I think she's about 500 years old", revealing IU's nickname; mountain god. (meaning she's lived as long as mountains have been around)

On this episode Yoo In Na revealed even though IU is 11 years younger, she talks to her about her problems.