Fireblood

Fireblood is Sena's sword.

The Unicorn Quest
Sena made it in Scythe's Silverorium and named it Fireblood. Afterwards, she let Claire borrow it.

Fire in the Stone
Fireblood was destroyed.

Trivia

 * Sena got Fireblood back from Claire in the third or second book
 * After Fireblood was destroyed, the unicorns gift Sena with a new sword, Clearcut.