B2ST's Junhyung, BTOB, and�Ha Yeon Soo have collaborated to reveal a special song for the viewers of their upcoming drama 'Monstar'!

Junhyung and BTOB's Minhyuk, Sungjae, Changsub, and Hyunsik who star as members of the idol group 'Men In Black' in the drama, and Ha Yeon Soo who plays Min Sae Yi. will lend their voices for the song "Past Days". This will actually be a remake of Yoo Jae Ha's original song, and will be a fresh modern take as a dance track.

"Past Days" will be the opening song for the premiere of 'Monstar' on the 17th and the track will be released on the same day!