While a monk with the Tendai school, he came across texts about Zen which had been brought from China. In 1189, he dispatched two of his disciples to China to meet with Zhuó?n Dégu?ng (?, 1121-1203), himself a student of the Rinzai master Dahui Zonggao. The disciples presented a letter Nonin had written describing his realization from practicing Zen on his own. Deguang apparently approved and sent a letter certifying Nonin's enlightenment. Nonin then started his own school, which he called the Darumash?, or "Bodhidharma school".
The Daruma-school depended on two sources for their teachings: early Chán as "transmitted on Hiei-zan within the Tendai tradition", with clear elements of teachings from the Northern School, and the Chinese Rinzai-school. The Chán-teaching of 'inherent awakening', or hongaku, influenced the Tendai-teachings. It explains
[T]he principle of non-duality between Buddha and sentient beings, or between nirvana and samsara. This principle was expressed in many ways, the best known being the dictum, 'The mind itself is the Buddha.'
Nonin did not adopt Ta-hui's form of Zen. His own style came from the Zen meditation practiced in Tendai, which resonates with the early Zen of the Northern school first introduced from China by its founder Saich?. He drew copiously from the Sugyoroku, which was studied zealously on Mt. Hiei. In this way he fused Zen and the teachings of the sutras (zenkyo itchi). He also incorporated into his doctrine and practice elements of Tendai esotericism (taimitsu). He did not engage in the practice of koan. The Zen of the Daruma school, as its texts show, distinguished itself in this way from the Rinzai Zen of the Sung period in the line of Ta-hui.
In opposition to this supposed diversity of teachings, Hee-Jin Kim states:
N?nin was the favorite among Japanese Buddhists to establish a "pure Zen" (junsui-zen) in the country over the traditional "mixed Zen"(kenju-zen).
The Bodhidharma School apparently drew a number of followers, but in 1194 the Tendai establishment requested that the government have it shut down. They accepted the proposal for the school "being 'incomprehensible' and circulating nonsense." His students continued the school for a brief time, but eventually they dispersed to study with D?gen or Eisai. In fact, Koun Ej? and Tetts? Gikai, both prominent students of D?gen to whom nearly all modern Soto Zen teachers trace their lineages, were originally students of Nonin's successors. The transfer of Dogen to Echizen in 1243 may in part have been due "to the fact that the Daruma-shu had a strong following in that province".