When his father, Yoshitsura was killed in the ranks in Yamato Province by Nobuhide TAKEDA under the instruction by Yoshinori ASHIKAGA in 1440, the position of the head of the Isshiki family was assumed by Norichika ISSHIKI, who was from the branch line and a favorite subject of Yoshinori.
永享12年（1440年）に父義貫が大和国の陣中で足利義教の命を受けた武田信栄により殺害されると、一色氏の惣領には義教の寵臣で庶流の一色教親が就く。