There are quite a few different anime genres out there, but a genre people might not know even existed is the yokai genre. To elaborate, the term "yokai" is a Japanese word that basically means ghost or apparition, and it's a subcategory of folklore from their country that was/is used to explain natural phenomena and the like, as the Greeks did with the Olympus gods.
Some classic yokai that people might recognize from other anime are Kappa, Tengu, or even Oni. There are tons of games that use these yokai pretty liberally such as the Persona series, the Nioh series, and the Animal Crossing series. And there are also manga involving them. But it's anime that arguably features the most prevalent and well-known examples of the yokai genre in pop culture.
10 XxxHOLiC
xxxHolic came out in 2006 and is all about yokai spirits, based on the manga of the same name. It follows one Kimihiro Watanuki as he goes through his day, plagued by his ability to see spirits. One day, the guy is mysteriously compelled to enter a strange house and encounters Yuuko, the owner of a store that grants wishes and someone who offers to take away his "curse" of seeing spirits in exchange for him working there.
XxxHolic is one of those series that has a lot of back and forth dialogue that really gets the mind going, and it puts a spotlight on a part of Japanese culture that not many Westerners know about.
9 Hozuki's Coolheadedness
From spirits to demons, Hozuki No Reitetsu (or Hozuki's Coolheadedness) is another popular series about the occult, this time with Hell as the setting rather than some strange lady's house. This story follows Hozuki, the chief deputy to the King of Hell, Enma, though most of the time Hozuki acts like Enma's babysitter or parent rather than his subordinate.
Hozuki's Coolheadedness is another episodic series that doesn't have a very strong overarching narrative, but more than makes up for it with the comedy and characterizations.
8 Mononoke
In this story, a man that's simply known as "The Medicine Seller" exorcises Mononoke, which is just another name for yokai. The clearest draw of this anime is the art style, which is gorgeous but takes a bit of getting used to.
Once viewers adjust to the unique visuals, they'll be immediately drawn into Mononoke's atmosphere and narrative, with each exorcism taking 2-3 episodes as the Medicine Seller works to learn the spirits form, truth, and reason in order to finally defeat it. It's a very symbolic and nuanced series that's not afraid to experiment.
7 Yo-kai Watch
The Yo-kai Watch game series is quite obviously comparable to Pokémon, but the gameplay is pretty widely different. In Pokémon, they collect Pokémon, but in Yo-kai Watch, Keita is quite literally collecting ghosts.
In any case, the games became popular enough to get an anime, and surprisingly enough, it's pretty good. For people who just want to see as many yokai as possible, or want to know what the overall tone of Yo-kai Watch is like before trying the games, this anime is a great place to start.
6 Mob Psycho 100
Mob Psycho 100 is one of the more action-packed yokai series, and also one of the most stylish. This series is created by the anime legends at Bones, and it follows the story of Shigeo Kageyama (who goes by Mob) as he learns what it means to grow up as the world's most powerful Esper.
This series could not be more focused on ghosts, though Mob is equally bullied by both spirits and some other absurdly powerful ghost hunters. While MP100 doesn't represent as many of the classic yokai as other series in the genre, it is by far the most fun to watch visually.
5 Mushishi
Technically Mushishi doesn't have any yokai in it. But the entities called Mushi might as well be yokai with how similarly Ginko goes about helping humanity deal with them.
Imagine if spirits acted like single-celled organisms, they'd be lifeforms that could interact with the world in odd and unique ways but have no goals, and no real purpose. Mushishi is far and away the most relaxing yokai series (though it does get scary at times), and it takes its time telling each and every one of its stories.
4 Natsume's Book Of Friends
A common trope of yokai series is that they tend to be pretty episodic: A new spirit every week, and a new problem to solve. Natsume's Book of Friends is no different, but it is likely the most perfected version of it. This anime is incredibly highly rated by those who watch it and by the anime community in general.
Natsume himself is a very interesting character, and his growing love for yokai and his progress with reconnecting to humanity is one of the biggest draws of the series. This anime has a lot to it, and luckily there are multiple seasons of it for people to enjoy.
3 Inuyasha
It's a safe bet that people who originally saw Inuyasha on Adult Swim and/or Toonami back in the day probably didn't realize how many yokai were in it. Inuyasha is a story of love between Kagome, a teenager in '90s Japan, and Inuyasha, a half-demon (technically a yokai) living in Sengoku-era Japan 500 years in the past.
Kagome ends up traveling the world with Inuyasha in order to regain the shards of the Shikon Jewel along with a fox-demon, a monk, and a demon hunter. For a lot of people, Inuyasha was their first experience with anime, and it's nice to be able to look back and see all the ways this show still holds up.
2 GeGeGe No Kitaro
Unlike most yokai series, GeGeGe No Kitaro is long. Really long. It's a long-lived beloved franchise that sadly lost its creator back in 2015, but thankfully his story lives on. There have been multiple seasons series, and all of them are 50+ episodes.
Kitaro is quite the beloved series in Japan, and for good reason. Kitaro has so many oddball characters, but by the time most viewers are 10+ episodes in, they feel like they're part of this weirdo family.
1 Yu Yu Hakusho
Lastly, there's one of the most well-known anime of all time, Yu Yu Hakusho. A story that starts out horrifyingly sad as Yusuke Urameshi comes to terms with his sudden death then gets incredibly hyped once Yusuke learns about being a spirit detective and starts to use his patented Spirit Gun.
Yu Yu Hakusho is another series that got a lot of westerners started on anime, and it was good enough to get them hooked. It's one of the best shonen series of all time, but it also deals with a lot of different yokai from Japanese folklore.