Red Velvet made their first appearance on a radio program through SBS's 'Kim Chang Ryul's Old School' on August 6 and discussed how they prepared for their debut and their first impression of other members.

Red Velvet said, "It has been one and a half years since the group was created with our current members.  We practiced for our debut song 'Happiness' for six months." They performed the song live for the first time since their debut on the show, receiving ardent applause.  

MC Kim Chang Ryul said, "How was your first impression of one another?"  Joy said, "I was scared of Irene," making everyone laugh.

She continued, "Irene is severely shy around strangers, so she does not laugh easily. But now I really like her."

Check out their performance below!