WARNING: The following contains spoilers for Demon Slayer Season 2 Episode 13, "Layered Memories," now streaming on Funimation, Hulu and Crunchyroll.
Demon Slayer's first episode began with an eerie and ominous tone meant to reflect the tragedy that befalls the Kamado family, but also to set the stage for the series' main antagonists: demons. A carnivorous, supernatural race, these immortal beings possess a bloodthirsty instinct to kill and feast on humans -- the few exceptions being Nezuko, Tamayo and Yushiro. Surprisingly, this concept draws many similarities to Attack on Titan.
While these two incredibly popular shonen series appear to be vastly different -- with Attack on Titan being a much grislier story -- upon closer inspection, it becomes clear that Demon Slayer's demon race has powerful abilities reminiscent of titan shifters.
For starters, both demons and titans have a desire to eat humans. While this is only truthful for pure titans, shifters can eat other shifters to gain their abilities. And with a lifespan of only 13 years, they must be consumed before the end of that timeframe to pass on their abilities. On the other hand, Demon Slayer's demons devour humans as a means of survival and to grow stronger. When they first transform into demons, they are faced with an extreme hunger that can only be satisfied by consuming humans. The more they eat, the stronger they become.
More accurately, the two species have regenerative abilities. Demons can heal serious physical injuries and re-grow entire limbs or even organs within several seconds. The stronger the demon, the faster their recovery time. For example, the Upper Ranks can regenerate almost instantaneously. In Attack on Titan, shifters -- as well as all other titans -- can also regenerate limbs and nearly any other injury. Some can be completely healed within minutes while more serious injuries, like re-growing limbs, take much longer. While this seemingly makes demons and shifters untouchable, they actually share a common weak point.
The one way to kill a demon is by aiming for the neck and slicing their head off, which can only be done with a Nichirin sword. These swords are forged from a unique ore that constantly absorbs sunlight and are the only weapons capable of inflicting damage on demons -- which coincides with their other weakness, being exposed to sunlight. Similarly, titans and shifters can only be killed by slicing through the nape of the neck. In regards to pure and abnormal titans, this cuts off the nervous system, but with shifters, the nape is also where the shifter's human body lies.
While this is seemingly where the resemblances between demons and shifters end, Season 2 Episode 13 of Demon Slayer reveals one more. Tanjiro's quiet rage following a senseless slaughter from Daki, Upper Moon Six, triggers a new memory from far in the past. As the hero questions Daki's ability to trample on human lives so easily, she is met with a memory of another Sun-Breathing user asking similar questions. But this memory doesn't belong to Daki or even her previous life as a human. Rather, it belongs to Muzan Kibutsuji.
As the Demon King and the first demon to come into existence, humans can only be transformed into demons with Kibutsuji's blood. Having received an exponential amount of that blood -- which greatly enhances their strength and power -- the Upper Moon and Lower Moon demons make up the 12 Kizuki and are the 12 strongest demons. This likely explains how Daki could access Kibutsuji's memories.
Attack on Titan fans might recall this ability as titan shifters retain the memories of the shifter they ate, while the founding titan can alter memories. But unlike demons, they also keep their memories from the time before becoming a titan shifter. Both demons and shifters emit an immensely powerful and intimidating aura, but are followed by great tragedy. In Demon Slayer, characters are killed and lose everything pertaining to their lives as humans before transforming into a demon, often against their will. And while many shifters are not formed by choice, they develop a lifespan of 13 years courtesy of the Curse of Ymir.