Sultan Ibrahim became a personal friend of Tokugawa Yoshichika during the 1920s. Tokugawa was a scion of the Tokugawa clan, and his ancestors were military leaders ("shōgun" in Japanese) who ruled Japan from the 16th to the 19th centuries. When the Japanese invaded Malaya, Tokugawa accompanied General Yamashita Tomoyuki's troops and was warmly received by Sultan Ibrahim when they reached Johor Bahru at the end of January 1942. Yamashita and his officers then stationed themselves at the Sultan's residence, Istana Bukit Serene and the state secretariat building, Sultan Ibrahim Building to plan for the invasion of Singapore.