HSF is a secret government organization in Z Mazinger. While little is actually known about them, they control a good portion of the Japanse Defense Force and recruit highly skilled individuals to help them control threats that are beyond the capabilities of conventional militaries. They appear to have a large amount of government funds supporting them, shown when Koji Kabuto and his family are given a 1 billion yen salary for Koji's cooperation.
With the threat of Dr. Hell looming and the Japanese Defense Force proving to be ineffective against him, HSF agents recruit Koji Kabuto and Gennosuke Yumi to combat Hell's Mechanical Beasts with the new mobile weapon Z Mazinger made from the salvaged body of the Olympus warrior Zeus. They also have Tetsuya Tsurugi and Jun Hono support Koji, especially after the Mechanical Gods make their prescence known and later recruit Sayaka Yumi to pilot Aphrodite A to assist Z Mazinger.