Kunai were the most common weapon produced by her family trade.
She had been playing stealth with her sister—thirteen years old and just turned chunin, Kanako had been eager to teach her little sister everything she knew. So when Tenten was caught hiding in the forge and playing with a kunai knife, Kanako was quick to lead Tenten to the training fields—to the dismay of their mother, and to the delight of their father once Tenten's aptitude from her father's side was found.
Soon, kunai were also the most common—and only—weapon in her hands.