Anime's more fantastical creations can often feel like they've come out of nowhere. Sometimes that's true - no one can explain the twisted origin of FLCL - but, in many cases, creators draw inspiration from ancient stories and legends.
Much of the real mythology in anime comes from Japanese folktales and traditions. Shinigami, which appear in Death Note (among other shows), are gods that perform many of the same duties as Ryuk and Rem, minus the whole notebook thing.
Other shows cast a wider net, using cultural tales from Europe, South America, and Africa. Without Norse mythology, the world would never received Ah! My Goddess.
Even if you already love a series, understanding the legends upon which it's based will give you a deeper appreciation for the artistic liberties the story takes.
Traditionally, Shinigami don't use mystical notebooks to carry out their grim work, and they are Japanese gods who determine mortals' fate. According to legend, Shinigami are spirits that lure humans towards demise, either by persuading them to take their own life or outright slaying them.
Surprisingly, the term Shinigami is actually a product of Japan's interaction with the Western world (most likely in the 18th or 19th century). Prior to then, Japanese tradition did not consider the loss of life to be an inherently bad thing. While the idea of these spirits still existed, they weren't sinister, as they assisted with a natural life process.
The Western influence on the idea of the Shinigami perhaps explains the creatures' resemblance to Grim Reapers.see more on Death Note
To create a vast world of unique creatures, Pokémon pulls inspiration from a wide variety of sources, such as ice cream, real-world animals, and even Japanese mythology. Jynx, an ice/psychic type Pokémon, is based on the Japanese legend of the Yamauba. According to myth, Yamauba are elderly witches who live in the mountains and target naive journeyers. The legendary beings' magical powers and preferred location account for the Pokémon's elemental composition.
Exeggutor is also based on a mythological monster. Jinmenshi are trees that bear fruit resembling raucous human heads. The fruit is said to have gone extinct after it was consumed in huge quantities. Why anyone would want to eat a fruit that looks like a human face is not explained. (Exeggutor, for his part, does not look especially delicious.)see more on Pokémon
African mythology is rarely featured in anime, so the 2017 children's show Onyankopon is in a league of its own. The show references an Akan folktale about Onyankopon the sky god, who used to live among humans, but retreated into the air after an old woman hit him in the head with a pestle she was using to mash yams.
The anime version of Onyankopon is a dancing cat. Like any true god, the logic behind his appearance is never thoroughly detailed, but speculatively, it could be because the "nyan" in his name is Japanese onomatopoeia analogous to "meow."
Onyankopon wants to use his dancing abilities to help humans with their problems, but he's afraid to go near them, as the pestle incident left him traumatized. Because of this, he sends proxies to help high school girls navigate issues like relationships and dieting. It's confusing, but sort of cute.
Interviews With Monster Girls features a variety of mythological creatures called "demi-humans." The cast includes a vampire, a succubus, and an ice woman, all of whom are trying to find acceptance at a Japanese school, despite having unusual bodies.
Most of the characters are cute, harmless versions of terrifying monsters. While most people think of vampires as bloodsucking demons trying to slay humankind, Hikari Takanashi is a peppy, energetic girl who uses a lot of sunblock and drinks government-supplied blood packs.
Kyouko Machi is a dullahan, one of the more terrifying figures from Irish mythology. Dullahans roam the Irish countryside at night, carrying their severed, rotting heads and indiscriminately leading humans to their doom. Sometimes, dullahans ride around on jet-black horses Sleepy-Hollow-style, but in other versions of the story, they travel in black coaches that move rapidly enough to set fire to the surrounding area.
This all sounds pretty dreadful, but you wouldn't know it from watching the anime. Kyoko - the show's resident dullahan - is a regular girl who carries her head to school and would never dream of slaying anybody.