is the third spiritual leader of the Sà Âtà  Zen school of Buddhism in Japan. He began his Buddhist life as a student of the Darumashà «'s Ekan, but later both became students of Eihei Dà Âgen's newly established Sà Âtà  school. Gikai received dharma transmission from Koun Ejà Â, Dà Âgen's successor, and later became the third abbot of the school's head temple, Eihei-ji. Shortly thereafter, he became embroiled in a leadership crisis known as the sandai sà Âron. Other monks contended that other students, namely Jakuen, Gien or Giin, had stronger claims to the abbacy. The controversy remained unresolved at the time of his death. His abbacy was unpopular with some monks because he introduced innovative practices aimed at making Sà Âtà  more palatable with the Japanese laity, which some claimed Dà Âgen would have frowned upon. However, he also had many followers, and eventually his innovations became the standard form of Sà Âtà  Zen. His leadership marked the first geographical expansion of the Sà Âtà  school when he moved with his followers to Kaga Province. Most notably, his disciple Keizan Jà Âkin became the second most famous figure in the school's history after Dà Âgen by generating mass appeal for Sà Âtà  Zen and ultimately spreading the teachings to all corners of Japan.
Tettsà « Gikai was born in 1219 in a rural area of Echizen Province called Inazu. His family was part of the powerful Fujiwara clan, specifically claiming descent from the famous General Fujiwara no Toshihito. Members of this extended family included prominent monks of the region. Others had formed bonds through marriage with the Hatano family, which was to become the primary donor to the early Sà Âtà  school. He became a monk at the age of twelve at a Darumashà « temple called Hajaku-ji, which was located close to the future site of Sà Âtà  Zen's main temple, Eihei-ji. His teacher was Ekan, a student of Kakuan, in turn a student of the Darumashà «'s founder Nà Ânin. His close connections to Echizen, and particularly its Buddhist elite, played a role in his importance to the early Sà Âtà  school.
Shortly after becoming a monk, Gikai relocated to Mt. Hiei for an unknown period of time for training, although he remained a student of Ekan. In 1241, most of the students of the Darumashà « joined Eihei Dà Âgen's early Sà Âtà  school, which at that time was centered at Kà Âshà Â-ji outside of Kyoto. Thus Ekan and Gikai both became students of Dà Âgen, although to an extent Gikai remained a student of Ekan simultaneously. In 1243, shortly after Dà Âgen and his followers had moved to Echizen where Eihei-ji would be built, Gikai was assigned to the important position of tenzo, or head cook. Dà Âgen considered tenzo to be suitable only for monks of high attainment, but on a more practical level Gikai was probably also better equipped to locate donors of food in his home province. About a decade later in 1251, Ekan gave dharma transmission of his Darumashà « lineage to Gikai realizing that he would soon die without a successor. However, he also urged Ekan to receive transmission of the Sà Âtà  lineage as well. Four years later in 1255, two years after Dà Âgen's death, Gikai accomplished this when he received dharma transmission from his former fellow Darumashà « student and Dà Âgen's successor, Koun Ejà Â.
In 1267 Tettsà « Gikai became abbot of Eihei-ji when Koun Ejà Â, the previous abbot, retired due to illness. Gikai's promotion to abbot was specifically requested by the two major patrons of the temple. Keizan Jà Âkin, who would go on to become an extremely important leader for the school, was ordained as a monk by Gikai in 1271 when Keizan was seven. The following year Gikai retired from his role as abbot, eventually being replaced by Gien, whose life and time at Eihei-ji is poorly documented. Gikai lived for the next 20 years caring for his mother near Eihei-ji and occasionally visiting the temple for various reasons. In 1280 he cared for his predecessor Ejà  in the days before his death. During this time, Ejà  apparently gave Gikai his robes, which he had in turn received from Dà Âgen. Nine days later Ejà  died, after which Gikai performed the funeral. Gikai also held yearly services to commemorate Ejà Â's death, and it was during this period that a conflict arose between him and the followers of Ejà Â's other successor Jakuen. The reason for the dispute is not clear. Jakuen himself had left Eihei-ji many years before in 1261. Whatever the grounds, Gikai ultimately permanently departed from Eihei-ji in 1287 despite personal support from the temple's major patron.
Gikai left Eihei-ji and traveled to the neighboring province of Kaga where he became the second abbot of Daijà Â-ji temple in 1293. The first abbot, Chà Âkai, was of the esoteric Shingon school and had probably known Gikai from his early years at Hajaku-ji, which was a Shingon temple that had hosted Darumashà « students for several years. Furthermore, the temple was patronized by Togashi Iehisa of the Fujiwara clan, most likely a relative of Gikai. Several students from Eihei-ji joined Gikai at his new temple, including Keizan Jà Âkin, Meihà  Sotetsu, and Gasan Jà Âseki. Two years after Gikai's arrival, he gave dharma transmission to Keizan. Three years later in 1298 Gikai passed on the position of abbot to Keizan as well, though he remained at the temple for the rest of his life. By 1306 Gikai's health began to decline. During this period he ordained all of the non-monk workers at the temple at his own insistence. He died in 1309. Keizan only served as abbot for two years after Gikai's death, after which the position was transferred to Meihà  Sotetsu. Shortly after, the patrons of the temple replaced Meihà  with a Rinzai monk for unknown reasons. Keizan wrote that this was a betrayal of Gikai, although Meihà  would go on to be reinstated as the abbot of Daijà Â-ji after many years.