Madara's brother Izuna and Obito share the same birthday (February 10) and blood type.
The Ame Orphans Konan and Yahiko share the same birthday (February 20) and blood type.
Kiba shares the same birthday as his nin-dog partner Akamaru (July 7), which is on the start of Tanabata, a Japanese star festival.
Nawaki died in battle the day after his twelfth birthday.
Kakuzu's birthday (August 15) corresponds with the astrological sign Leo, who rules the heart, the organ Kakuzu collected from defeated enemies.
The Head Ninja of Kumogakure attempted to kidnap Hinata Hyūga on her third birthday (Hyūga Affair).
Naruto's birthday (October 10), was Health and Sports Day in Japan when his character was conceived. The holiday, however, was later moved to the second Monday of October in 1999.
Sasori shares the same birthday (November 8) as the creator and author of Naruto, Masashi Kishimoto. Additionally, his birth date makes Sasori's Western astrological sign Scorpio, and his name (蠍) means "scorpion".
Rock Lee shares the same birthday as Bruce Lee (November 27).