Seven Is Nana

When counting in Japanese, shichi is the typical word used for the number 7. However, in normal conversation, you will almost never encounter a Japanese person say shichi in any other context. The problem lies in the fact that Japanese people don't actually like the word shichi, as it sounds too similar to shi, the counting word for 4, which also sounds like the word for death. Being a superstitious people, the Japanese really, really hate invoking death every time they count.

Nana is one pronunciation for the number 7 in the Japanese language, and is the one more commonly used. In anime and manga, it's sometimes used as a feminine name with possible double meaning. If a character appears with the name Nana, expect Meaningful Name.

Keep in mind, however, that if you want to describe seven things, seven objects, or seven people then you'll be using different words entirely. Yeah...Japanese is hard.

One, Two, Three, Four, Go is a Sister Trope. See also Numerical Theme Naming.

Anime and Manga

 * Elfen Lied features experimental subject Number Seven, or "Nana" as her father figure calls her.
 * Loveless has a Hikikomori called Nana who only briefly shows up in the anime but plays a larger part in the manga, and her name likely refers to her dependence on computers. She's referred to as "Seven" in the Tokyopop manga release... until volume eight, when they switch to Nana.
 * Both stars are named Nana in the manga Nana, and live in apartment 707 -- effectively using this trope as its entire premise. One of them is called "Hachi" (short for Hachiko, but also meaning eight) to differentiate between them.
 * In Shichinin no Nana (Seven of Seven), a girl named Nana is split into seven personality fragments.
 * And all those fragments get names that describe them and start with Nana.
 * Best of all, the primary Nana's Japanese voice actor is also named Nana (Nana Mizuki, as a matter of fact).
 * In Puni Puni Poemi, the seven Aasu sisters are all named after numbers, in reverse age order. So the youngest sister is named Hitomi (from "hito" - one), and the oldest is named Nanase.
 * Kodomo no Omocha's Sana is named after her birthday, March 7.
 * In Katekyo Hitman Reborn Tsuna is occasionally associated with the number 27. It's on his door, as well as the mitten form of his X gloves. Tsu sounds like two, and na is seven. Thus, 27.
 * Made cuter by the fact that his mother's name is actually Nana and his father is Iemitsu. The last syllables of their names makes Tsuna's name.
 * Saki of Futari wa Pretty Cure Splash Star is associated with flowers (hana); naturally, her birthday is August seventh (ha - eight, na - seven).
 * In the first episode of Heartcatch Pretty Cure, Tsubomi is seen wearing a shirt with a 7 on it. This has two possible meanings -- the fact that it's the seventh season of the series, or an Actor Allusion to her seiyuu.
 * Nanaho Kinjou in Best Student Council is the seventh child of the Kinjou family. Her Killer Yoyo has a seven emblazoned on it, and one of her blouses has a seven on it as well. Taking the number theme further, her nickname for her six older brothers are their birth numbers.
 * In Othello, Nana receives a mix tape with "For 7" on it. She then realizes it means "For Nana".
 * The main protagonist in Battle Royale is Shuya Nanahara, nicknamed 'Wild Seven' because of his surname.
 * In Area no Kishi, Nana Mishima, a.k.a "Seven", was referred to by her elementary school football jersey number, which just so happened to be "7".
 * Nanami in the name Lucia Nanami means "seven seas".
 * Playing off the all ready established pun of "Nonoriri" referring to, Nono is also a pun by bring next to "nana".
 * Nanael from Queens Blade also counts, since almost all the angels from that series are named after numbers with the Hebrew suffix "-el" included. (Her best friend and senior, Hachiel, has number eight as her preffix in her name)

Fan Works

 * An unnamed backgrounder character from Daria referred to officially only as "Cheerleader #7" has picked up the name Nana, short for Natalie Nash, in Fanon.

Video Games

 * Mega Man X Command Mission has a reploid named Nana as your Mission Control, with the number seven displayed prominently on both her breasts.
 * Nanako in Tsukihime/Kagetsu Tohya. Originally... well, not quite originally since she was a human once with a presumably human name. Er. Anyway, previously, her name was Seven, in English, as she's the spirit of the Seventh Scripture; a fusion weapon created from her soul and the horn of a unicorn monster. Arihiko translates that to Japanese, Nana, and then adds a feminine ending to it. There, Nanako the horsegirl, spirit of a BF Harpoon Gun that shoots pages of the Bible. Yep.
 * Higurashi no Naku Koro Ni gives us.

Real Life

 * "Na na na" in a song is sometimes shown as the Arabic number 7 in karaoke. One example of this is Konjiki no Gash Bell's sixth ending.
 * Nana Mizuki milks this trope for all it's worth with her singing career up to a point that she charges $77 for her concert tickets.
 * And she voices the Windows 7 OS-tan, Nanami Madobe (her names meaning "seven"(-mi) and "by the window").
 * Actually nanami can mean 777 too. So 777 by the window. Yeah...