Sai Yamanaka is a supporting character in the anime and manga series Naruto. Initially introduced as a member of Team Kakashi, he replaces Sasuke Uchiha after his defection. Sai is a skilled ninja from the secretive 'Root' division of the Anbu and is known for his emotionless demeanor and mastery of ink-based jutsu. Over time, he learns to connect with his teammates and develops a more open, caring personality, eventually becoming a valued friend and strong ally.