1st Edition Monster Manual. When a pair of mated dragons had offspring, any attack on the young dragons caused the father and mother to attack the intruders with a ferocity bonus of +2 to hit and +1/+3 on clawing/biting damage.
1st Edition Monster Manual II. If a male cheetah's cubs are threatened he will attack at a +2 to hit and do +2 Hit Points damage per attack.
In the Ravenloft setting, Rudolph van Richten went Papa Wolf on the Vistani band that kidnapped his son, and then hunted down the vampire who'd hired them to deliver the boy. It was revealed in Van Richten's Guide to the Vistani that the originally kindly and very forgiving doctor's curse of vengeance upon that particular Vistani clan for what they did is the reason why they can never rest in one place for more than a day or two. Because with his curse that "the undead take you" as they took his son to the undead, every surviving member of the clan is forever hunted by the undead until Van Richten lifts the curse with his forgiveness.
In Warhammer 40,000 the Space Wolves Chapter of Space Marines are this towards civilians and innocents, and will hunt down and destroy anyone who hurts one - even other Space Marines or the Inquistion.
The Salamanders not only share the Space Wolves feelings about civilians and innocents, it is their primary purpose and objective, and are the only known Space Marine chapter that makes protecting civilians their mission in all things; anyone harming the ordinary humans of the Imperium or threatening them is rather prone to dying horribly from the fire-based weapons they favor.
Kill one of Sanguinius's Blood Angels (ergo: Sons) and he WILL break your spine. Likewise, if you hurt Sanguinius, the Blood Angels will tear you apart.
Most Clans in BattleTech look down on the unnecessary deaths of lower-caste civilians not as empathy for the suffering of innocents but as a needless waste, a concept they despise. Clan Ghost Bear, though? Hurt any of their people and they will end you. Just ask the Word of Blake or the Motstånd, a sepratist terror group operating in Rasalhauge. Both dared to use mass terror tactics that indiscriminately hit civilians and soldiers, whereupon the otherwise slow-to-act Bears promptly turned on them and messily ground them into bloody paste. The Ghost Bears are traditionally very tightly knit and embrace familiarity and even familial ties more than other Clans, so daring to attack any Ghost Bear is a great way to get lots of big angry people in Humongous Mecha and Powered Armor breathing down your neck in a hurry. Khan Bjorn Jorgensson basically held this view during the Alshain Avenger crisis, soundly crushing the renegade Black-Dragon-backed forces when they dared strike at his people on their Inner Sphere homeworld and accepting a truce after discovering and snuffing out the guilty parties responsible for the invasion.
Varanae generic RPG supplement Monstrum 1. Cerberus are a type of three-headed dogs. Parents will fight to the death to protect their young.