The Branded

As we explicate runes in Terrakal, we first must figure the Arcana Unearthed Runechildren. Runechildren are those who, at fifth level, in place of their sixth level accept a brand from... something. The runechildren are selfless, not working toward their own heroism. Per Monte Cook canon they are forces of good. Sarel the litorian was a runechild - although, interestingly, we are not so informed about the Hanavere Trinity.

Which is not to assume all Runechildren live in mutual concord. In [the past of] Diamond Throne two runechild siblings went west and founded Verdune and Thartholan: two realms, not one. Verdune would, a few decades later, ban magic which magic includes ... runes. (The dramojh invasion in their turn would fail to observe this ban, but we are getting ahead of ourselves.) This hints that more than one rune-inscribing entity exists.

Yes there exists a rune god: Vekik. AU / DT is a structurally atheist game; Vekik is nothing more or less than a reified Pythagorean statement (we'll say the same for Johrd). Vekik is evidence for this continent having no clue as to what runes are.

There also operates a runepriest cult. They seek to make runechildren by hand. I think they're closer the mark. Mike Mearls' Mystic Secrets sketched out which backstory might make what sort of runechild.

Overall - and this is clearest with Mearls - what makes a runechild in this land does not work in accordance with what its people need most, nor with the land herself. It is, then, not The Green making them. Also of note is that they quit showing up after Sarel, and only came back after the end of the dramojh. (Although if we accept Mearls, the anti-runechild Herald did continue to appear, making deals with the Dark, often against the dramojh.)

From the AU perspective I must conclude with the dragons, that the runechildren are tied with draconic interests. If the runechildren are "good" it is only to the extent they are altruists. The movie Serenity should explain sufficiently to all comers that perfect selflessness is not perfect goodness. Or, hell; just look in AU itself at the Champion class, even the Oathsworn.