Cosette

"In the neighborhood she was called the Lark. People like figurative names and were happy to give a nickname to this child, no larger than a bird, trembling, frightened, and shivering, first to wake up every morning in the house and in the village, always in the street or in the fields before dawn.

"Except that the poor lark never sang."

-Les Misérables, Volume 1, Book 4, chapter 3

Cosette is a character from Victor Hugo's novel Les Misérables and the musical play by the same name.

As a child, Cosette is adopted and raised by Jean Valjean after her mother, Fantine, dies. As a young woman, Cosette is the love interest of the student Marius.

In the Novel
When Cosette is still very young, Fantine pays the Thénardiers to care for her daughter while she works in another town. The Thénardiers, however, spend Fantine’s money, while Cosette is forced to work as a servant in their inn.

A few years later, Jean Valjean comes to rescue her, having promised Fantine he would do so just before she died. He finds Cosette in a forest, fetching water in the middle of a dark night, and helps her carry the bucket back to the inn. The two immediately begin to bond, and Valjean finds he is glad to have Cosette to care for and protect, as her presence prevents him from lapsing into his former criminal ways. After escaping to Paris, they go into hiding in a convent, where Cosette attends school for several years.

After Cosette completes her education, Valjean moves to a real house so that Cosette can experience life outside the convent. While taking nightly walks in their new neighborhood, Cosette and Marius begin to see each other on the street and fall in love. However, Valjean becomes jealous of Marius’ affections, and he stops walking with Cosette. Marius sees Cosette again when she and Valjean deliver clothes and money to the Thénardiers. Marius convinces Eponine to help him find where Cosette lives. Finally having a chance to speak to each other, Cosette and Marius begin to meet every night in the garden without Valjean knowing.

When Cosette reveals that Valjean is planning to flee to England with her, Marius leaves out of grief and fights at the barricade. Valjean rescues him, however, and reunites Cosette and Marius, who get married six months later. Valjean begins to drift away from Cosette to protect her from his criminal past, but Cosette comes to visit him just before his death.

In the Musical
Cosette's role is perhaps the least changed between the book and musical of any Les Mis character. The only real difference of note is that the musical skips directly from her rescue from the Thénardiers to her young adult life.

In Badfic
Cosette is sometimes pushed out of the way to allow Marius a chance at romance with either Eponine or one of the other revolutionary students. This is, unfortunately, not difficult for badfic authors to do, considering her already minor role during the scenes involving the barricade, especially in the musical. Nonetheless, Cosette/Marius remains a very popular pairing in its own right.