Takasu was a native of Sakuragawa Village, (currently part of Inashiki, Ibaraki), and graduated from the 35th class of the Imperial Japanese Naval Academy, where his classmates included future admirals Nobutake Kondō and Naokuni Nomura.

Takasu returned to England again in December 1930 to serve as military advisor on the ambassador’s staff, where he recruited Frederick Rutland to work for the Japanese Navy for a second time.

He was promoted to rear admiral on November 15, 1934 and reassigned to head the 3rd Bureau of the Imperial Japanese Navy General Staff, which was in charge of military intelligence.

An outspoken opponent to the Tripartite Alliance between Japan, Nazi Germany and Fascist Italy, he was a member of the naval faction led by Isoroku Yamamoto and Mitsumasa Yonai opposed to war with the western powers.

From 1936-1937, he commanded the First Carrier Division, which was active in combat in the early stages of the Second Sino-Japanese War, and was a naval advisor to the fledgling state of Manchukuo in 1937.