Arcadia

"'You don't get it, Incubator. This Seraph does your job better than you could ever do, and no one has to suffer for it. No one except for you.' - Mariko to Kyubey after meeting Arcadia"

General Information
Arcadia (アルカディア - Arukadia) is the Seraph belonging to Mariko Takekawa that makes it's first appearance in Mariko Magica and then in all subsequent stories that Mariko appears in as well.