The Titans currently reside within the dimension known as Final Space. They are also said by Nightfallto be responsible for the destruction of the universe in the future, when Mooncake opens the Final Spaceportal in a fit of rage.
It is also known, that they are sacrificed to like Gods, this is seen in Chapter 3, when the High Helpers concoct a battle-to-the-death arena called, the Deathcropolis, in order to make sacrifices to the Twelve Titans.
It is revealed in Chapter 8 that the Titans are a race of cosmic beings seemingly born with the sole purpose of infecting the universe with chaos. Bolo was alone among his brethren in that he realized there was a better way. In a final act of defiance and rebellion, Bolo used his powers to close the portal between Final Space and the mortal universe. Imprisoned by his fellow Titans for his rebellion, Bolo has been sealed in a great cube in his own realm, reaching out with his mind to find mortals he can warn about what horror opening Final Space will unleash.