"Ghost Story in a Boys' School") is a 2021 South Korean web series featuring an ensemble cast consisting of the members of boy band Treasure—Choi Hyun-suk, Park Ji-hoon, Yoshinori Kanemoto, Kim Jun-kyu, Yoon Jae-hyuk, Asahi Hamada, Kim Do-young, Haruto Watanabe, Park Jeong-woo, So Jung-hwan, Mashiho Takata, and Bang Ye-dam.

Its plot centers on a group of 12th grade students in a boys' school who try to solve the mystery of their class' resident ghost.

A series of spooky events drove the students to suspect each other while trying to solve the mystery of their class' resident ghost, who might simply be posing as one of their classmates.

Both of these theme songs are performed by Treasure and were released on 15 February 2022 through the CD version of the band's first extended play The Second Step: Chapter One.

[13][14] A Christmas version of "BFF (Best Friends Forever)" was released earlier on 24 December 2021 through the band's official social media accounts.