Two brothers, riven by conflict in the War of the Weave.
(Items in Bold are things that aren't canon, and just exist in the Cyclic Plane Storyline.)
Davix (left) and Callan (right) are half-brothers. They bear the same mother, though Davix's father, a le-matoran, died during the process of creating him. Callan was created three years later after their mother found love once again with a ta-matoran. Their parents were devout followers of The Hexarc, and Callan and Davix grew up in Bazryghan with the teachings of the Elemental Council close at heart.
Korrothis, the original island that was the home of the Elemental Council within the Matoran Universe, which broke away after Teridax took control of the Matoran Universe. The island crash-landed on Bara Magna and, after the Reformation, the city of Bazryghan grew around it.
Korrothis was being repaired so that it could fly through space again, this time aiming for a world discovered in the old Great Being archives called Atmos Magna. It needed many hands to make this possible, including those of Callan and Davix. While they would much rather have fun with their friends, a sense of Duty pervaded the place.
Callan and Davix were transformed into Toa after a pipe burst and sprayed them both with Energised Protodermis. Their co-workers were not so lucky. After being taken in for training under the Elemental Lords of Air and Fire, Gringat and Tahu.
Davix's guitar became his Toa Tool, from which he could channel his powers, including some Sonic techniques. Callan gained a pair of blades derived from the tools he was using just before the incident. Callan and Tahu bonded especially well, so far as for Tahu to name him his Son, and an Archon of Fire. Callan fell in love with another of Tahu's apprentices, Madura. Davix became very good friends with Gringat's son, Nilmador, but mainly got up to trouble with him.
As time passed, Korrothis left Spherus Magna. Nilmador became the new Le-Nui based in a new council chamber in Bazryghan. Then, tragedy struck as the Ignika shattered from overuse, killing Mata-Nui and Tahu in the process. Callan was elected as the new Ta-Nui, but they were dark times they had to govern. Following the loss of Mata-Nui, many of the Matoran Universe's original inhabitants suffered a wasting disease called the Soulplague. Few survived. Fewer survived with their minds intact.
A few centuries after the plague passed, the Knights of Spherus Magna began to act oppressively towards the peoples of Spherus Magna. Academic study of "Holy" Great Being technology became outlawed, and creators of new kanohi masks and the like were arrested. Use of mixed elemental powers amongst the population became more widespread as well, and this was also clamped down on. Tensions rose between the elemental council and the knights, most notably between Nilmador and his sister Elithrar, who commanded the knights.
Several members of the original Elemental Council broke away with Nilmador and Gloriana and created a new faction based in the Great Jungle called the Druids. This faction believed the development of elemental powers and technology should not be restricted, and opposed the KoSM in an event known as The War of the Weave, so called because two elemental councils arose that opposed one another. Callan stayed with the KoSM, and Davix joined Nilmador.
Three years into the conflict, in midsummer, Callan met blades with his brother. Subduing and defeating Davix, Callan hesitated. Madura intervened, and, after fully seeing the evils the KoSM had commited and hidden from him, joined the Druids. In doing so he gave up the status of Ta-Nui (this belonged to Ackar). The Druids eventually won the war and Nilmador was crowned Turaga-King of the Matoran Empire.
Their entry: Xmastrex, Toa of Christmas Trees
These guys are still built, though might be missing a few parts nowadays (exo force arms are at a premium for my MOCs...)
Davix's lower leg design is one of CallanLOF's.
Long after making these guys, I joined up with Callan, Ben Cossy and Shadowgear6335 to run a livestream series called the Broken Axles. It was fun while it lasted, though trying to coordinate between three very different time zones was extremely taxing for all of us, and we all had education to worry about...
Curiously, of we four, in my storyline Callan, Shadow, Gringat and Cossy weren't friends. Shadow and Callan never met, Shadow and Cossy never met, and Gringat basically condemned Cossy to death during the Battle of Bara Magna. Gringat did meet all three of the others though.