[3] In 2009, he contributed two soundtracks from Boys Over Flowers including the acoustic version of "Because I'm Stupid""[4] and "A Thing Called Happiness".

[5] He, then released a DVD entitled Goodbye Yoon Ji-hoo, marking the end of his character role in Boys Over Flowers, and coming back as the leader of SS501.

[7] On June 7, 2011, Kim released his solo debut mini album, Break Down,[8] exceeding 70,000 pre-ordered copies in just 10 days.

The album has been certified Gold by the Recording Industry Association of Japan (RIAJ) after selling more than 100,000 units to retailers.

[26] His third Japanese single "Tonight" topped the Oricon Daily charts with 101,818 copies sold,[27] and taking the number two spot by the end of the week.