Vivian

Vivian is Mario's fifth party member in Paper Mario: The Thousand-Year Door.

At first, Vivian is one of the Shadow Sirens. They battle Mario in Boggly Woods for Flurrie's necklace in Chapter 2.

However, at Creepy Steeple, Mario fights Doopliss, a Duplighost. He steals Mario's body and identity, leaving Mario as a shadow.

When Mario returns to Twilight Town, he finds Vivian searching for a Superbombomb. Mario finds it for her and Vivian asks him what he is doing here. Mario tells her about Doopliss and Vivian agrees to help get his body back.

When Mario and Vivian finally reach Doopliss' room in Creepy Steeple again, they battle him along with all Mario's old partners, who think Doopliss is Mario. Vivian realizes that the one she was helping was Mario, but she joins him anyway because Mario was much kinder to her than Marilyn or Beldam. At the very end of Mario's adventure, Beldam and Marilyn end their villain activities and promise not to mistreat her again.

Outside of battle, she possesses the same ability Bow has in Paper Mario, in which she hides Mario and his team in the shadows.

Vivian possesses the cloaking/transparency ability that Bow had in Paper Mario, but works in a more interesting effect: instead of literally turning invisible, Vivian can pull Mario into their shadow, where they can hide. This allows them to get past objects that move over them, and avoid sight from enemies and their attacks. Vivian possesses the strongest magic of any partner in the game, and is often thought of as the best partner in the game thanks to her fiery powers and the ability to burn enemies.

At first, Vivian is a Shadow Siren working with her sisters Beldam and Marilyn. She is often blamed for things she didn't do, resulting in a bit of an inferiority complex. In Chapter 2 they are all sent to destroy Mario in the Boggly Woods, and take the Magical Map. The Sirens, however, fail at defeating Mario. In Chapter 4, when the doppelgänger Doopliss steals Mario's name and body, Beldam loses the superbomb and blames Vivian who is then ordered to find it. Mario finds the Superbombomb and gives it to Vivian, making her feel better. However, Vivian is unaware that the shadow comforting her is Mario, so after Mario tells her the story about his problem, Vivian decides to join Mario and help his shadow get back his name and body. However when she finds out that the shadow was Mario, she feels stupid and leaves him right before fighting Doopliss. Later she comes around and decides to help Mario (and actually joins the party) because of the kindness he had given her earlier, or perhaps because she has a slight crush on him.

Gender
There is a controversy about Vivian's true gender in the original Japanese version; some claim that she is a pretty boy or bishounen, much like Zoisite of Sailormoon fame. However, in the Japanese version the "Three Shadows Group" uses the word majotachi, which refers to a group of sorceresses, i.e. females, words like her, she, and sisters are also used. Unlike most characters that undergo major changes during translation, Vivian maintains her (female) name in both the English and Japanese versions. Beldam often calls Vivian "Man" but this could be Beldam's way of insulting Vivian. More telling is that the menu information describes Vivian as a male though this also could be a joke showing that Mario (who is supposedly journaling the adventure) misheard that Vivan was male.

In a rough translation of the character description of Vivian:

"One of the shadow group, Vivian appears to be a girl but is really a boy."

Also in a rough translation of Goombella's Tattle of Vivian:

"That's Vivian. Of the shadow group, she's the youngest sister... er, brother."