God Sigma

Space Emperor God Σ is an anime series aired from 1980 to 1981. There were 50 episodes. It is also referred to as "God Σ Empire of Space" and "Space Combination God Σ".

The year is 2050 and an energy crisis is Earth's main concern. A brilliant scientist in Trinity City develops the Trinity energy, a new source of energy powerful enough to supply the entire world. The alien empire of the Elda learn of this energy and plot to seize it by force. They attack Earth's space colony on Jupiter's moon of Io and occupy it. Meanwhile, the Trinity energy has been applied to three giant robots that combine to form God Σ, a mighty robot led by its main pilot, martial artist Toushiya Dan. With its mighty sword, it now stands between the peace of Earth and the power of the Elda forces.

However, later in the series it's revealed that the Elda forces came from the future, where Earth attacked Elda's home planet. Using an advanced time-machine the Eldans try to seize the secret of Trinity energy to save their home planet.

Tropes used in God Sigma include:

BFS/Cool Sword: Musouken!
Calling Your Attacks
Combining Mecha: The robots Kaimeiou, Rikushinou, and Kuuraiou combine to form God Sigma.
Improbable Weapon User: Spin Saucer!
Luckily, My Shield Will Protect Me: God Shield! Or, in Super Robot Wars Z, GODDO SHIIIIIIELDO!!
Name's the Same: Shows up in the original Z with God Sigma Gravion and one possible romanization of the name of the alien race is Eldar.
Names to Know in Anime: Tomokazu Seki and Tessho Genda
Power Trio: Toshiya Dan, July Noguchi, Kensaku "Kiraken" Kira
Ramming Always Works/Incendiary Exponent: Wing Attack! Big Wing!
Throwing Your Axe Always Works: God Tomahawk!
Shock and Awe/Whip It Good: God Sting!
Super Robot
Super Robot Wars: The Series is included in the Playstation 2 game Super Robot Wars Z, in which Toshiya's voice is performed by Tomokazu Seki (of Mobile Fighter G Gundam fame). It will return in Z2.
Zorro Mark: Sigma Breast! *God Sigma fires a mark that looks the Greek letter Sigma at the enemy* Musouken! Senkougiri!