After his home planet were destroyed by space ronins, the last gun-wielding cyber-samurai must track down and kill an old foe who intends to erase all life and create a new universe using a dangerous alien weapon.

I really like this concept; take a Japanize?Samurai?movie and set it in space.

You have an order of Samurai who are kind of like the ‘Jedi Order’ in star wars.
they are men of honor and keep the law.

You have an evil warlord who sends his minions to attack the lead character’s planet.

Now the Samurai must go on a journey of honor to avenge his people’s death.

You?would create a couple mini-bosses?(To use a video game term) that he must fight through first.
Maybe each mini-boss is on a different planet or space station and after he defeats them
the lead character would gain a clue as to the whereabouts of the evil warlord.

All culminating in the final showdown. The epic duel between the lead character and the warlord.

One possible big reveal: Perhaps the evil Warlord
is actually the lead character’s brother, who everybody believed was dead.

They fight. Good guy wins. Roll credits.

I think the whole universe-destroying weapon seems to come out of nowhere and could actually be a distraction
from the more personal story of revenge and honor; however, if you are determined to tell that story, it could be added in.