(Bestiary) Arhaj
Arhaj are merciless semi-aquatic raiders who ransack, extort, and occasionally massacre coastal settlements. Though they're sapient, their motivation is extremely simple and overwhelmingly powerful: due to their fast metabolisms and a few quirks of brain chemistry, arhaj are constantly, ravenously hungry. To them, humans are simply livestock ruling over other livestock.
Stats
HD 3, Df leather, Mv normal / swim 2x normal, Mr 9, Dmg bite 1d6 plus chill, or by weapon. Solitary or school (1d6+2).
Sea Devil: Arhaj take half damage from cold and are immune to pressure hazards. They can breathe both air and water, though they find air unpleasant over long stretches.
Chill: Anyone struck by an arhaj's bite attack must Save vs. exhaustion or suffer a momentary numbing chill, falling prone unless they choose to drop a random held item (if they have one).
Look: Hulking, naked 9' shark-orcs, fat but sleek. Rough blue-black skin, reflects light strangely when wet. Webbed hands and feet. Giant, serrated upward-pointing tusks. Gills suck noisily while on land.
Arms: Always edged weapons, mostly bone axes and shell-studded mauls. Some use javelins, or rusty tools looted from land-dwellers.
Manner: Callous but calm when satiated. Laconic. The hungrier they are, the more erratic and less patient they become. A starving or enraged arhaj is just a shark with legs.
Tactics: Encircle and shred. They sometimes try fancier approaches, but it never lasts long once they can smell blood.
Logic and Hunger
Imagine going grocery shopping on an empty stomach. (You may not need to imagine it. If you've ever been poor or had issues with executive function, you've been here.) As you work your way down your shopping list, aisle by miserable overlit aisle, you're fighting a constant, low-level battle against your own biology, resisting the urge to stuff your cart with more than you need or more than you can afford. Worse, the environment you're in is actively cooperating with that urge, poking and prodding at all those lower impulses, begging you to give in.
Take that feeling and double it. That's how an arhaj feels on a good day.
Arhaj don't pay for groceries, of course. What tempers their hunger is the anticipation of hungers yet to come. They exist on a constant knife edge between the gnawing ache in their guts and the knowledge of how destructive it would be to give in. So, instead of eating humans and their ilk directly, they extract tribute - never currency, only meat. It's more sustainable than devouring a fishing village every month or two, and it burns fewer calories.
Of course, it wouldn't hurt to devour one village, just every now and again, y'know, to keep the rest scared and motivated... And that's how it gets you. The hunger infects even the cold logic of survival. What distinguishes the smart arhaj from the starving ones isn't whether they think like this - they all do - but how often they act on it.