Each key has its own name and world in which it leads.

Vongola - Katekyo Hitman Reborn

Titan - Shingeki no Kyojin

Game Life - Sword Art Online

Butler - Kuroshitsuji

Ninja - Naruto

Flames - Ao no Exorcist

Gynn - Magi

Eggs - Shugo Chara

Ghouls - Tokyo Kushu

Dollars - Durarara

Alchemy - Fullmetal Alchemist: Brotherhood

World - Hetalia

Martial Arts - Kenichi History's Strongest Disciple 

Magician - Negima!? Neo