The Requiem Blaster was forged by Solus Prime, the Thirteen's fabled weapon-smith, for Megatronus Prime to defeat Unicron.
It was an extremely powerful Weapon able to blow through the mountain behind Solus's testing area. After the test she voted to destroy it as it was to powerful. The vote was 7 to 6, it would be destroyed, and only Solus could ever put it back together again. After the defeat of Megatronus Prime, now known as The Fallen, the Requiem Blaster was lost.
It is later revealed that the weapon was placed in the Thirteen's transport ship. After it was seemingly deserted, the ship drifted through space. The sheer mass of the weapon drew space junk towards it over the years it was engulfed in more, and more junk, until it formed and became the gravitational center of a Planetoid, Junkion.