Yokais were characters featured in tokusatsu products in my childhood along with kaijus.
We had two tokusatsu drama series with yokai characters featured which were strikingly impressive: Akumakun (1966-1967: 26 episodes) and Kappa No Sanpei Great Operation Yokai (Yokai Daisakusen) (1968-1969: 26 episodes).
Both of them were based on the manga products created by Shigeru Mizuki and produced by Toei Company.
Akumakun is about a boy nicknamed Akumakun (akuma means devil/demon/satan; kun is a Japanese honorific title) who can summon a devil named Mefisto and fights against evil yokais and kaijus with his help.
Kappa No (no is the word showing possession) Sanpei is also about a boy named Sanpei gifted with supernatural ability from the kappas whose member Sanpei saved depicting his fights against evil yokais during his trip searching for his mother captured by those yokais.
All of them were produced by Toru Hirayama, Toei producer, including Giant Robo (1967-1968: 26 episodes) and Masked NInja Akakage (1967-1968: 52 episodes).
The boys who starred Akumakun and Kappa No Sanpei were Mitsunobu Kaneko (1957-1997) and Yoshinobu Kaneko (1955-present) respectively. Although both of them are Kaneko and their first names also sound alike, they are no kin.
Mitsunobu is also well known for his starring role as Daisaku Kusama in Giant Robo and Yoshinobu also gained popularity for his leading role as Aokage (blue shadow) in Akakage.
Incidentally Sanpei’s fellow kappa Rokubei in Kappa No Sanpei was acted by Fuyuhiko Maki who also regularly played Shirokage (white shadow) in Akakage.
Many monsters featured in the Toei and P Production were characterized by their weird appearances unlike the Ultra Kaijus.
The Tsuburaya products, based on Eiji Tsuburaya’s concept to avoid showing children anything ugly and weird, stuck to featuring monsters which are more straight-ahead while, as you know well, Tohl Narita’s monsters with statuary looks got to make the monsters attractive enough so that they are highly reputed even today.
On the other hand, the Toei and P Production monsters had no restraints like that unlike Tsuburaya that had to defend the Tsuburaya brand.
As the result, it is undeniable that the weird but unique-looking monsters which appeared in those series ended up having their attraction in their own way.
As a matter of fact we had other characters as much popular as kaijus back then which were yokai.
Yokai (literally suspicious mystery/suspicious mysterious being; kai is the same Chinese character as kaiju while the latter means mysterious beast) is a specter which looks like a goblin or imp which had been traditionally talked about in Japanese folktales while kappa featured in Episode 41 of Ultrasevenis one of the yokais.
Along with the anime Gegege no Kitaro (1968-1969) based on the manga created by Shigeru Mizuki well known for his yokai manga with much popularity among people, yokai characters have been frequently featured in manga and anime products alongside of kaijus in Japan although kaijus managed to win much more popularity.
Yokais were featured even in movies such as the 1968 Daiei (known for the original Gamera series) movie Yokai Daisenso (Yokai Major War) in my childhood and I remember I fully enjoyed it as they had their own attraction.