유희열의 스케치북
On August 1, 2019, via Instagram, Kim and Son announced that they were collaborating as a project duo under the name HoooW (), a portmanteau combining one character from each of their given names. As HoooW, they have appeared on "" and "You Hee-yeol's Sketchbook" and performed as guests at Psy's summer concerts. On August 16, they released the digital single "Game Over" ().