A trend I’ve noticed in progression fantasy series is that often the main way that people get stronger is by killing stuff. This is pretty common in LitRPG’s where killing living things to get their experience points is the way to level up. Even when there are other methods of leveling up, killing things will still be the most effective way of getting stronger. This can culminate in series where the protagonist either literally or metaphorically “devours” others to gain their strength.
Power from death is a fairly basic idea to the point where most people don’t even question it. The idea of getting experience and level grinding probably came from video games and RPG’s where it’s the most common method of leveling up the player character. In a way, it can be rather silly that killing fifty bears lets you level up your charisma stat, but that’s just kind of how it goes. Non-LitRPG series usually have some other justification for why killing things makes someone stronger such as eating souls, absorbing mana, or gaining the favor of gods through sacrifice.
Sometimes it’s not necessarily killing opponents that brings power. I’ve read cultivation series where it’s the experience of fighting in actual life or death scenarios that pushes someone to become stronger. There might be a magic reason such as the soul forcing itself to grow when in danger or it could be that a dangerous situation forces a character to improvise and try new things. The character might have a dangerous technique that they’ve been struggling to master, but now they have no choice other than to use it. It might also just be the case that practical experience always provides a unique learning opportunity that training and sparring can’t compare to.
Something that doesn’t come up too often in these kinds of series is the ethics of killing things purely so that someone can grow stronger. This is especially so since often it is all living things, including humans, that can be killed for strength. Some series acknowledge the moral implications by having more villainous characters be indifferent to whether their experience points come from people or monsters while heroes stick with monsters. They can also show how gray a protagonist’s morality is by having them also not be particularly concerned about the fact that their strength comes from murder.
On big advantage for this method of growing stronger is that it can provide justification for a protagonist who advances rapidly compared to others. In these types of settings, stronger monsters and people provide more experience towards leveling up. It’s common for protagonists to have to fight enemies that outclass them in various ways and have to figure out a way to come out of a highly dangerous situation. This allows the protagonist to get stronger much faster than what is expected without even needing to give them some special power or talent to justify their rapid growth.
Depending on how its implemented, a strength through killing system can have its downsides. One of which is that this method of getting stronger can feel rather arbitrary, especially if it’s the only method of getting stronger. Some LitRPG’s I’ve read make it so that even if someone’s skill set is based around crafting or healing, they can still only level up by killing monsters or people. It’s rather silly that someone whose class is Tailor has to figure out a way to apply their skills to combat if they want to become a better tailor. I personally prefer it when simply doing tailor related tasks is how you level up such a class.
There is also the issue of things feeling too much like a video game. You can wind up with characters literally level grinding by killing large amounts of weaker enemies and gaining strength that way. This can actually be fine if the goal is to show how people exploit the system to their advantage, but it can also make the setting feel less “real”.
A good example of this kind of murder for power system is the Demonic Devourer series. The protagonist, Evelyn, is a bioweapon with the unique ability to absorb some of the strength of what she kills. This is actually unique in this setting since most people level up by completing quests given to them by the System. Evelyn was essentially designed to be a sociopath with a desire to grow stronger written into her biology. This series does a good job of showing how messed up a person would need to be to enjoy killing people and consuming their strength in a never ending desire to gain levels.
Power through killing is a common way to grow stronger in progression fantasy series. The setting might run off of video game logic or have other justifications for why death makes someone stronger. The end result is often a system where killing things often becomes the main goal for anyone who wants to level up. In general, power through death is a fascinating trope with ethical implications that fit right in with LitRPG’s.