Wild Mass Guessing for Wave Motion...Space Battleship Yamato 2199:
Many of the new characters will die in the battle against Domel.
Celestella will die seeking revenge for Mirenel.
Wolf Fraken will become Harlock, for one continuity.
Mamoru Kodai will become Harlock, just like in the manga of the original seriesAnd when this is found out, the Gamilas surrender unconditionally.
The Cosmo Force reverse engineered captured Gamilas technologyMore specifically, what would become the Wave Motion Gun, shock cannon and wave motion shield (that they couldn't make work correctly without Starsha's core, having only huge shock cannons), a sublight-only version of the wave motion engine, and, most evidently, pre-Yamato energy weapons (just confront the turret of the Yukikaze◊, so distinctive that it's enough to allow medical personnel to identify its model from an unspecified but otherwise similar class of destroyers, and the Kirishima◊, with the most widely used type on Gamilas ships◊.
We know that the Cosmo Force stopped the Gamilas twice at Mars before the invaders switched tactics to raids and planetary bombs (Yuki openly states the victory of the First Battle of Mars in the first episode, with the background image implying it was a costly victory, and Okita is often called the Hero of the Second Battle of Mars, implying another but very close victory), and that the Cosmo Force still uses more traditional firearms and missiles, devastating but with very short range, so they had some wreckage to study. Nothing easier that Cosmo Force, after an hard-won battle and one where they had nearly been conquered, decided to reverse-engineer the enemy technologies to being able to hit them at range (something that didn't work really well due the enemy having Deflector Shields), closing range faster (something that did work due either the Gamilas shields offering imperfect protection against solid objects or the shells being just that powerful), defending from enemy firepower with the wave motion shield (failed due the lack of reactors powerful enough) and fielding more powerful weapons (the shock cannon, that, without sufficiently powerful reactors, could be mounted only on battleships and only one per ship, with inadequate cooling technology preventing it and its support systems from being miniaturized enough for turret mounts).
Then, when Earth was about to either surrender or launch an escape mission, Yurisha showed up with the plans for a proper wave motion engine, with its support systems enabling to miniaturize the shock cannon to mount it on turrets (and human mind developing the Wave Motion Gun), and Sasha provided the core to make the thing work...
At the end of the series the Yamato will be welcomed home by a few surprise shipsNamely this◊, a couple of these◊ and a small squadron of these◊, with the Andromeda being laid up.
If the series gets a second season, Serizawa will be executed for war crimesBecause after the defeat of the White Comet Dessler would show up with his fleet, point out that there's no peace treaty with Gamilas and threaten to resume retaliation for the unprovoked attack at first contact, with things evolving in a formal peace with Gamilas giving symbolic reparations for the bombing on Earth and Serizawa given to Dessler to pay for his crimes. And get executed after a completely regular trial.
Yamato was not the first choice for the voyage to IskandarIzumo was, repurposed after Yurisha brought the plans for the warp engine, but was destroyed during construction by a Gamilas raid specifically targeted at her.
After the loss of Izumo, seven ships were laid up in hidden locations, equipped with shock cannons and wave motion engines: Arizona by the US, Bismarck by the European Union (with protests from France, UK and Italy for the name: France because it's the name of a German ship, UK because they have a more glorious naval history, and Italy because the logic of naming the ship after Europe's mightiest battleship falls before the superior firepower of the four Littorio-class battleships, but the name stuck because of the battleship Bismarck's fame and the British alternative name, Prince of Wales, being that of a ship with a lackluster record), Borodino by Russia, four unnamed warships by China, South America, India and Africa (their naval history had less glorious names to choose from) and Yamato by Japan under the relic of the old battleship.
Due to shortages in resources for the other ships and works on the Yamato having been slowed down due a sudden redesign, it looked like the choice would fall on either Arizona or Borodino as they would be completed first, but then Serizawa produced the plans for the wave motion gun that the Yamato had just been redesigned for, and, being the only ship that could be completed with it in time for Sasha's arrival with the wave motion core, the Japanese vessel was ultimately selected.\\ In the end the other battleships were completed after the Yamato left for her voyage, with cores copied from Sasha's one and redesigned with wave motion guns. And the rest of Europe laughing at the Brits when India named their ship Prince of Wales (a battleship with that name had been sunk while defending them, after all). And the Chinese battleship, completed with Japanese assistance (the price being putting a Japanese captain on her), was the Andromeda.
The White Comet Empire is indirectly responsible for the devastation of EarthBecause their continued attempts at invading the local galaxy cluster keep most of the non-garrison Gamilas fleet busy in the Lesser Magellanic Cloud, and when the war against Earth started they just didn't have the forces to spare to wipe out Earth's fleet in five minutes, show up in orbit and demand a surrender.
Had Starsha not sent the plans for the wave motion engine or the Yamato got destroyed before leaving, Humanity would have been saved anywayBy either surrender after losing the last hope or invasion and quick conquest. In both cases the Gamilans would have either restored Earth or shipped Earth's population to another inhabitable planet, whichever better suited Dessler.
Kaoru's life will be in extreme danger when the Yamato returns to Earth.For the rest of the crew, returning to Earth means a heroes' welcome. But Kaoru Niimi is at this point the only person left alive in the crew who has first hand knowledge of General Serizawa's plan and orders behind the mutiny. Serizawa's involvement in starting the war may have been hushed up in the name of solidarity and public morale but if he were linked to an attempt to derail the Iscandar mission, then his career; at very least would be destroyed. The Iron Tiger has not gotten where he is without a strong degree of ruthlessness and sacrificing one woman's life to ensure his survival would be a price he would be quite willing to pay.
The Gamilas originally came to Earth to share the later albums from their greatest band in history, known on Earth as the CrescendollsAnd they became militaristic and started conquering other worlds in the first place precisely to prevent others from kidnapping them again.