Information:
re:Japan is a supergroup that was originally put together to sing a cover of Sakamoto Kyuu's "ashita ga aru sa", around the same time that the Ulfuls covered it. They also did a cover of "Bittersweet Samba" afterward, as their second single. Every single person in this group is already established for something.

Downtown is an enormously popular comedy group. They host their own comedy shows, as well as Hey! Hey! Hey! Music Champ. They've both been featured in several commercials, and Hamada has even recorded music with famed producer Tetsuya Komuro (under the name "H Jungle with T"), as well as with Makihara Noriyuki.

Kokoriko is another comedy duo, who has also hosted a few various TV programs.

Hazama Kanpei is an actor and "talent" (a term for someone who is a general TV personality, hosting various shows, etc.)

Fujii Takashi is a comedian, as well as a singer/dancer who has released several singles. He also hosts music/variety show "Matthew's Best Hit TV", as his alter ego Matthew Minami.

London Boots ichi gou ni gou are a comedy group consisting of two brothers. They've hosted several different variety/comedy programs (the most current of which is "London Hearts"), and they've also released a couple of singles.

Yamada Hanako is also a comedian personality. She has been involved in several TV programs, as well as some anime voice acting (you'll understand when you hear her voice).

Lastly, Higashino Kouji is a comedian who has collaborated with Downtown on the show "downtown no gotsuu ee kanji", and at one point also helped host popular variety show "waratte ii tomo". He's also appeared in a few dramas.