The Song of Pelinal, v3

When Huna, whom Pelinal raised from grain-slave to hoplite and loved well, took death from an arrowhead made from the beak of Celethelel the Singer, the Whitestrake went on his first Madness.

Michael Kirkbride, who wrote Knights of the Nine, wanted to say that Huna "shared a tent" with Pelinal, but Bethesda thought that would infringe on the fact that the player was reincarnating him.

On the "Insane cyborg from the Future" part:

The Song of Pelinal, v2

[And then] Kyne granted Perrif another symbol, a diamond soaked red with the blood of elves, [whose] facets could [un-sector and form] into a man whose every angle could cut her jailers and a name: PELIN-EL [which is] "The Star-Made Knight" [and he] was arrayed in armor [from the future time].

Here's where the Arm Cannon comes from

The Song of Pelinal, v1

he was Pelinal the Whitestrake because of his left hand, made of a killing light;

All this is from in-game sources, with Michael Kirkbride himself adding a few years later:

Pelinal was and is an insane collective swarmfoam war-fractal from the future, you betcha.