Aratake Sansei served as a bushō during the Sengoku period. He was a retainer of the Itō clan of Hyūga Province.
The Aratake clan became servants of the Itō from the time that the Itō moved from Izu Province to Hyūga around the early Kamakura period. The Aratake were from a lineage of jizamurai, or provincial samurai, known as one of the Four Guardian Clans of Tonokōri. During the Sengoku period, many members of the Aratake served as magistrates or officials of the bakufu. Sansei was particularly well-known for his knowledge of both the military and literary arts. He was deeply trusted and relied upon by his lord, Itō Tadasuke, the eighth head of the Hyūga-Itō. Sansei was well-versed in waka, exchanging poems with Asukai Masayasu who came from Kyōto to visit him.
Sansei actively served in a battle against the Shōnai-Hongō clan and, in 1520, was appointed as the lord of Katsuoka Castle on the front lines. In 1526, after the Indō rebelled against the Higo-Sagara clan, Sansei deployed and contributed to its suppression.
In 1533, however, after the early death from illness of Sukemitsu, Itō Suketake (Tadasuke’s younger brother) revolted, forcing Sukemitsu’s chief retainer, Fukunaga Sukeaki, and his three sons to kill themselves and then occupied Tonokōri Castle. This owed, at least in part, to Suketake’s resentment toward Suekaki for his high-handed conduct of affairs of the clan. Sansei backed Sukemitsu’s younger brother, Itō Sukekiyo (later known as Yoshisuke) as the successor to the clan. After Sansei defeated Suketake’s forces, Suketake took his own life.
In 1534, in a battle at Niiroin-Taka Castle, Sansei was killed in action after a violent clash against members of the Mera clan leading a revolt.