Any child of Regalia learns quickly that of all guards, the river is the most supreme. It is ruthless, fast-acting, and asks no questions. It needs no light nor sword to do its job, nor rest or motivation. No, the river merely is. And they are lucky that it is on our side of this world.
Bartholomew of Sandwich was clever to pick this land for Regalia. For where humans were not built to live in this darkness, the river is a force of nature, and it makes for an excellent shield.
Yet even as the river lies as a moat between us and our enemy, we must not think it a friend. It is an ally of convenience and location, and it does not discriminate.
Trust a gnawer, or trust the river? The gnawer is fueled by hatred, but the river only moves as it always does. That is a question for you to ponder. But just as the stories tells of children gutted for approaching the vile rat, so do the stories tell of the fools who have thought themselves masters of the water; and, as price for their hubris, the river has torn these fools asunder, never to be seen again.