Spectra Swallow

 is Serge's best weapon in. It has a silver shaft with two glowing blades that shift with the colors of the rainbow attached at each end. In order to acquire it, a player must have at least one summon of each color. (This is best done after defeating the six dragons to get the six most powerful summons in the game. The player must also have at least one Rainbow Shell in order to forge this item. Once this item is received, the following process be completed in order to forge the it.

After defeating the Dragons, Serge must return to his traditional, Human form, which requires the Dragon Tear from Fort Dragonia. Once there, all crystals are activated and no enemies remain. Travel to the top of the Fort, enter the door present there, and watch the cut-scene. This returns Serge to his original body, after which, he must travel to the Sea of Eden, find his way to FATE, and defeat the supercomputer. Doing so awakens the Dragon Gods, who fuse and declare war on El Nido.

Proceeding these events, Serge travels to Marbule in Home World and speaks to the guy in the cave where the Black Dragon resided. He provides Serge with the Master Hammer. Switch to Home World at Opassa Beach, head to Termina, and speak with Zappa's counterpart with Zappa in the party. Together, the Zappas forge the Rainbow Axe. Smith Spirit can be called to craft the Spectra Swallow at this point, using the Rainbow Axe, Rainbow Shell Shards, and 21,600 G.

Trivia

 * Swallows are based on, an oriental weapon which literally translates to blades on a staff. The name Swallow likely emerged due to the shape of the blades which strongly resemble the
 * Swallow may be an allusion to Crono's katana in, which also bears the name Swallow.
 * Spectra-, in the weapon name, could be an adaptation of specter, which is a synonym for ghost. However, it is more likely that Spectra- is shorthand for spectrum, since this weapon is made from the Rainbow Shell (a rainbow is a spectrum of color).