Our investment securities, consisting of debt instruments at amortized cost, debt instruments at fair value through other comprehensive income and equity instruments at fair value through other comprehensive income, totaled ¥32,112,677 million at September 30, 2024, an increase of ¥1,962,840 million, or 7%, from ¥30,149,837 million at March 31, 2024. The increase in our investment securities was primarily due to an increase in our holdings of Japanese government bonds.
Our bond portfolio is principally held for asset and liability management purposes. It mostly consisted of Japanese government bonds, U.S. Treasury securities and bonds issued or guaranteed by foreign governments, government agencies or official institutions.
Our debt instruments at amortized cost amounted to ¥352,863 million at September 30, 2024, an increase of ¥36,471 million, or 12%, from ¥316,392 million at March 31, 2024, primarily due to increases in our holdings of Japanese government bonds, Japanese municipal bonds and mortgage-backed securities.
Domestic debt instruments at fair value through other comprehensive income amounted to ¥10,946,884 million at September 30, 2024, an increase of ¥1,550,939 million, or 17%, from ¥9,395,945 million at March 31, 2024. The increase was primarily due to an increase in our holdings of Japanese government bonds. As for our foreign debt instruments at fair value through other comprehensive income, we had ¥15,510,616 million of foreign debt instruments at September 30, 2024, which was an increase of ¥890,377 million, or 6%, from ¥14,620,239 million at March 31, 2024. Most of our foreign debt instruments, including mortgage-backed securities, are issued or guaranteed by foreign governments, government agencies or official institutions. The increase was primarily due to increases in our holdings of bonds issued by governments and official institutions excluding U.S. Treasury and other U.S. government agency bonds and mortgage-backed securities.
We had ¥3,702,091 million of domestic equity instruments and ¥1,600,223 million of foreign equity instruments at September 30, 2024, for which we made an irrevocable election at initial recognition to present subsequent changes in fair value in other comprehensive income under IFRS 9 “Financial Instruments.” Our domestic equity instruments, which consisted principally of publicly traded Japanese stocks and included common and preferred stocks issued by our customers, decreased by ¥696,819 million, or 16%, from ¥4,398,910 million at March 31, 2024. Net unrealized gains on our domestic equity instruments decreased by ¥624,639 million, or 20%, from ¥3,197,856 million at March 31, 2024 to ¥2,573,217 million at September 30, 2024. The decrease was primarily due to a decrease in the fair value of publicly traded Japanese stocks. Net unrealized gains on our foreign equity instruments increased by ¥46,006 million, or 4%, from ¥1,108,894 million at March 31, 2024 to ¥1,154,900 million at September 30, 2024, mainly reflecting favorable conditions in overseas stock markets.
We have no transactions pursuant to repurchase agreements, securities lending transactions or other transactions involving the transfer of financial assets with an obligation to repurchase such transferred assets that are treated as sales for accounting purposes.