Yasutomo was the son of Asahina Bitchû no kami Yasayoshi. He originally served the Imagawa and held Kakegawa castle in Tôtômi Province. He destroyed Saigo Masakatsu when the latter rebelled in 1561. He sheltered Imagawa Ujizane when Ujizane was forced to flee Suruga as a result of a Takeda invasion and surrendered Kakegawa to the Tokugawa as per an agreement between Ieyasu and Ujizane. Yasutomo ended up at Odawara castle in Sagami province and his eventual fate is unknown.