Room 707 is a location in NANA. It's the apartment where Nana Osaki and Nana Komatsu live at the beginning of the story.
Nana Komatsu, not wanting to annoy her boyfriend, Shouji Endo, any longer, decides to search for an apartment. She is able to find a cheap old building that over looks a river, but Nana Osaki is already being shown the available apartment. After a bit of an argument, the two Nanas decide to share the apartment.