SAAY is the voice behind "Happiness" for the 'Nobody Knows' OST.

"Happiness" is SAAY's first time singing for an OST, and her dreamy vocals are the perfect tone for the lyrics about remorse, loss, revenge, and the search for happiness through trials. The music video above follows Cha Young Jin (played by Kim Seo Hyung) as she navigates her personal life while searching for an infamous serial killer.

Listen to SAAY's "Happiness" above! Have you been watching 'Nobody Knows'?