Cassiopeia

Cassiopeia is the official fan club of South Korean band, TVXQ. It was named after the 5-starred constellation, Cassiopeia. Its counterpart in Japan is called BigEast. The fan club was formed on April 23, 2006, a few years after the group's debut. The official fanclub color is pearl red, signifying passion. April 23 is celebrated by fans as Cassiopeia Day as this is the day when the fanclub member registration initiated.

Membership
Cassiopeia is the largest fan club in South Korea, with over 800,000 members registered on their Daum fancafe, Yuaerubi. Its membership totalled to over 920,000 members internationally in 2009. In 2008, Cassiopeia was listed in ‘Guinness Book of Records’ for "World's Largest Fanclub". Cassiopeia was again listed as the "World's Largest Fanclub" in 2011. International fans of TVXQ who do not belong to the official Daum fancafe or have SMTown membership also call themselves Cassiopeia.

Charity
Cassiopeia shows their support in TVXQ's name by sponsoring and donating to charities, building schools and parks as well as community centers across Asia. These are referred to as "fan projects".
About five hundred people from Yunho's Japanese fan page “Let’s Go Together” participated in raising

money and on July 29, 2011 donated 500,000 yen (approximately $6,400 USD) to Japan’s earthquake relief. Special towels were created on the fan page, “Let’s Go Together” and these towel packs were sold to each member of the on-line community to raise donation money. This was the third time they have donated money, accumulating to a total of 1.5 million yen (about $19,200 USD).
Members of Yunho’s Japanese fan blog ‘ONE‘ donated nearly $20,000 to a social welfare association in his hometown of Gwangju, celebrating his 27th birthday. His fans in China also volunteered their time with the less fortunate, and donated enough money to support a young girl living in a difficult situation in China so that she can live comfortably for an entire year.
In 2012, fans of Yunho built a library in his name. It opened on March 24 and is located on the second floor of Chungam Elementary School, and the library provides students with books, bookshelves, desks, writing supplies, and more. The library includes 1,688 books.