Here is the page where you can check out all the open and taken characters. Click on their page and read their info then go to the form and appy.

10 Seals
Amie Ayame-Taken
Kisaku Furi-Taken
Renai Tokiko-Taken
Renai Sonoko-Taken
Eien Midori-Taken
Uranai Subaru-Taken
Kamikakushi Umeda-Taken
Tenkawa Sorata-Open
Eien Kaworu-Taken
Shimiya Toshio-Taken

Four Muses
Ete, summer-Taken
Avaia, spring-Taken
Laurana, muse of autumn-Taken,
Hiviarla, winter-Taken

Gate Keepers
Utique-Taken
Esti-Open
Fleur-Taken
Silvara-Taken
Pierial-Open
Daei Lian-Taken
Marcelle-Open
Zern-Open
Zacri-Open

Dark Order
Queen Paiseas-Taken
Yuzukiele-Taken
Sorenza-Taken
Aisling-Open
Keela-Taken
Tilleul-Open
Aidameh-Open
Ouri-Open
Tarkis-Open
Oviel-Taken
Cadiner-Open
Eritou-Open