A few Titans solve many issues, including the Reapers.

There has always been a section of the galaxy closed off to all of the galactic Civilization. Known simply as the Montoken Region and encompassing 20% of the galaxy, no one has dared stray close to this region. It supposedly is home to monsters of all kinds, dangers straight out of nightmares, and even leviathans that roam the space hunting everything. It has been so dangerous that even the Reapers have avoided the area throughout all their cycles.

What Happens when dozens of species, hundreds of civilizations, and thousands of different lifeforms evolve in the safety of this Region? Answer: They war against each other until an outside force makes them all work together. That was what happened, the Prethoryn Scourge forced the nations of the Montoken arm to work together.

Now in 2900s, these nations, United under the Galactic Commonwealth of Nations, look to explore and expand outside the Montoken arm. They will encounter the 'powerful's, the misfortune, and those seeking to bring the galaxy under their heels. It's a good thing the Commonwealth has a bunch of Titans however because some people are going to need a laser down their throats.