BTS, also known as Bangtan Sonyeondan or Beyond the Scene, is a seven-member K-pop group based in Seoul, South Korea. The group was formed in 2013 by Big Hit Entertainment and debuted in 2013 with the single "No More Dream".

Since their debut single, BTS has become one of the most popular and influential K-pop groups in the world. They released many successful albums and singles, and toured the world, performing to crowds of devoted fans. BTS is known for their popular music, energetic performances, and high-quality music videos.

BTS members are also recognized for their unique personalities and lifestyle image, which have attracted a large following on social media. BTS are considered one of the most influential K-pop groups of their generation, and have won numerous awards and accolades for their music and performances.

"ARMY" are the fans of BTS, a South Korean K-pop group. BTS fans are referred to as "ARMY" in reference to their official slogan "Adorable Representative MC for Youth". Members of ARMY are very dedicated to BTS and their music, and are actively involved in promoting and spreading their music online and on social media.

ARMY is known for its strong online community and online projects to support BTS, such as music award voting campaigns and social media trends. ARMY members are also known for their creativity, producing online content such as fanfiction, fanart, and music remixes.

ARMY is considered one of the most active and passionate fan groups in the music industry, and continues to grow and support BTS as they continue to perform and release new music.

BT21 is a collaboration between BTS and Line Friends, a merchandise company based in Seoul, South Korea. BT21 is a line of merchandise such as plush toys, clothing, accessories, and stationery, all inspired by the unique characters created by BTS members.

Each member of BTS participated in the creation of BT21 characters, which represent their own personality and style. Characters include RJ the little teddy bear, Koya the little monkey, Mang the little alien, Shooky the little cookie, Tata the little alien, Chimmy the little puppy and Cooky the little bunny.

The collaboration was launched in September 2017, and BT21 products have become very popular with BTS fans and the K-pop community in general. The products are available at many online and in-store stores, including Line Friends and retailers such as Uniqlo and Zara.

The collaboration between BTS and BT21 is considered one of the most successful collaborations between a K-pop group and a merchandise company, and continues to grow and develop as a popular brand around the world.