If you're looking for manga similar to Tenchi Muyo! War on Geminar, you might like these titles.
The year is After Colony 195, and the Gundam boys have taken a stand for eternal peace by deciding to destroy their robotic weapons, Gundams. The peace is broken, however, when Mariemaia Khushrenada, who claims to be the daughter of the late Oz leader Treize, kidnaps Relena and declares a war of independence against the United Earth Sphere Nation. Perhaps it’s time to pull those Gundam units out of retirement.
The year is 2025. Earth is engulfed in the crossfire between massive warring alien life forms that leave annihilation in their wake. While searching for clues about his past, Ao is caught in an attack and forced to fly a giant humanoid fighter craft to save himself and his island. Fragments of the teenager’s origin come to light when a hostile shape-shifter seeking revenge on Ao’s missing mother—who vanished two years after his birth—targets him instead. Consumed with learning how his machine of war is connected to his mother and the monster that now pursues him, the young pilot will fly full throttle into combat zones without hesitation.
In this stunning twist on the tale of Code Geass, this alternative reality manga series supposes the following question: What if Nunnally had acquired the Geass power instead of her brother Lelouch? In the aftermath of becoming one with the doll-like energy form "Nemo," Nunnally becomes pilot of the Knightmare frame Mark Nemo and engages in a violent battle with the forces of Britannia. But this is only the beginning of Nunnally's nightmare...
Kawakami City is famous for its strong dedication to its samurai ancestors. A healthy fighting spirit is always valued and it's even an important factor for success at school. Yamato, a second year student from Kawakami High school, is always with his close friends (4 boys and 3 girls). They have all known each other since they were young and have done many things together. While they have many other friends, this group of seven is a close-knit, inseparable group. They even have a secret base where they meet. With the new semester, they welcome two girls into their group and shortly after things begin to change...
The hapless crew of the Nadesico is between the powerful Earth Federation forces and the mysterious Jupiterians. They have journeyed out to the planet Jupiter in hopes of rescuing Captain Yurika, but what they don't know is that she may not want to be rescued. How can a lone battleship survive against the amassed power of two planets?
It is Universal Century 0088. Haman Khan has claimed Axis as Neo-Zeon and rages war on both the Federation and the remaining Anti-Earth Union Group (AEUG), in order to resurrect the Zabi Family Dynasty. Meanwhile, fourteen-year-old junk collector Judau Ashta encounters the ship Argama, and with the help of his friends he plans to steal their Gundams. However, because of Judau's skills and unique Newtype abilities, he is instead entrusted with the AEUG’s newest weapon: the Double Zeta Gundam. The clash of the Newtypes continues as together Judau and his friends form the first Gundam Team.