Nindo Master Tessai (忍道師「鉄斎」Nindoushi Tessai) is an important character and the teacher of Sho and Kazuma, and the father of Aya. The creator of Nindo (忍道 Shinobi Ways), Tessai combined the Ninjutsu arts with mastery over Ki (気 energy); the power of creation itself. With these arts he would create many great and powerful skills, including a powerful ultimate secret technique that a power hungry Kazuma sought after.
Tessai was an Oboro-ryu shinobi master from Japan's olden times. A master of Ninjutsu, Tessai would go to create Nindo, the ultimate combat form combining Ninjutsu with mastery over the cosmic power of Ki. With these skills, he gave birth to various new techniques. Because of their power, Nindo was passed via Isshi Souden(一子相伝; tradition of secrets passed from father to son). However, Tessai had a daughter named Aya. Even so, he would still teach her.
As the years passed, the Shinobi bloodlines began to thin out due to the constant wars. Tessai, on one of his travels found two baby twins; the eldest he named Kazuma, due to his loud cry and keen senses, and the younger he named Sho; who always smiled as he was carried by the man he would come to love as a father. Tessai already had a daughter, Aya, but needed a son to inherit the full scope of his art.
For fifteen years, Tessai trained the brothers in Taijutsu (体術 Physical sciences and techniques), Tohjutsu (刀術; swordsmanship), and Ninjutsu. As for Aya, he trained his beloved daughter in Shinjutsu (心術; the Arts of the Spirit). But eventually he noticed Kazuma had a dangerous side deep within him. His worse fears were realized when he realized that Kazuma rejected the teachings of the Art of Peace, and sought only strength, demanding to learn the Ultimate Secret Art of Nindo. Tessai refused, prompting Kazuma to leave the school, while Sho and Aya continued their studies without him.
Eventually, Tessai would pass away, having not named a successor to his art. But not before he taught the secret to his daughter Aya; a secret she would pass onto Sho, who would become Tessai's successor.
- The circumstances between Tessai and Kazuma mirror that of Street Fighter's Goutetsu and Akuma; A master of a great art of immense power which holds a technique so powerful that it could destroy the user. For Tessai's Nindo it was the "Nyorai" technique, and for Goutetsu, the Shun Goku Satsu.
- According to the official Prima guide to PS2's Shinobi, Tessai and his students are Oboro as well.