MBK, formerly CCM now Pocketdols or whatever tf.
In the mid to late 2000s they were THE place to a girl group to debut an be successful, even before idols really took of. The SeeYa was big and one of the most vocally talented groups ever, Davichi was big and arguably the most vocally talented duos ever, T-ara goes without saying. Even SG Wannabe is/was a legendary group.
Jiyeon was an It Girl and one of the best visuals of her gen
Minkyung was a popular visual and COULD SING
Nam Gyuri was an It Girl
And of course ending fairy Chaeyeon
Not only that but Haeri (Davichi), Yeonji and Boram (SeeYa) were inarguably some of the very best vocalists of their generation.
SEEYA was ruined because of the heavy preferential treatment towards Nam Gyuri created such a discord that she left the group. as bad as people find the Miss A - Suzy situation, or the I've Wonyoung situation to be, SeeYa had that way worse in terms of favoritism, so much that the other 2 ostracized her. There was a public back and forth between Nam Gyuri, SeeYa members and the company after she left the group. She got replaced by another girl. That girl left the group too. Brought back Gyuri for their last album where she was overwhelmingly centric again. Disbanded.
Then they had the audacity name their new girl group THE SeeYa.
Davichi: hightailed it out of there once their contracts are up and are still kicking as a beloved duo even today.
T-ara: don't even get me started.
DIA: a mishandled mess and Chaeyeon was done so dirty by them 100x over
I believe they technically don't exist as a company anymore and as a Queen's, very happy for their downfall 
