Nadia: The Secret of Blue Water (1990)
Studio Gainax, Dir. Hideaki Anno and Shinji Higuchi
Opening “Blue Water”, performed by Miho Morikawa
all-timer anime opening
You can almost make an internally consistent Studio Gainax Mecha Anime Unified Timeline, but the one hitch is that Gunbuster and Evangelion both start in 2015 and portray a very different status for Earth and Humanity.
Maybe Nadia is the branching off point for both. In one timeline humanity investigates the Atlantean technology in the Nautilus and by 2015 has homing lasers, photon torpedoes, and degeneracy reactors. In the other timeline humanity finds the Atlantean base in Antarctica, investigates the body of Adam, and by 2015 has armored cyber kaiju.
Maybe have the closed timeline loop of Evangelion Rebuild erase the Second and Third Impacts from history, returning things to normal by 2015...just in time for the Space Kaiju to invade.
In any case, there's a pretty straight throughline from Diebuster to Gurren Lagann. When Lal'c and Nono draw on "hard work and guts" they're unwittingly tapping into the energy source that would later be scientifically codified and technologically harnessed as Spiral Power.