^ Note the nicknames: Miki is "Nonaka-shi" ("Ms. Nonaka"), Maria is "Marian", and Haruna O. is "Ogatan". It's important to note because the nicknames they use amongst themselves and on their blogs often supersede the nicknames that were assigned by management. That's how we got "Maachan", after all.
EDIT: "Nonaka-shi" is an odd one. There is definitely a story there, even though we might never hear it.
https://en.wikipedia.org/wiki/Japanese_honorifics#Shi