In 1401, when Kagenaka was 14 years old, due to the death of his foster father, he succeeded to SHIRAI-NAGAO clan which was a family of senior vassals of UESUGI clan.
14歳であった応永8年（1401年）、養父の死によって上杉氏の重臣である白井長尾氏を継ぐ。