Rosario-Kuuga.

( Tsukune Aono 15 boy who makes funny jokes and wants to make everyone smile but he see an old ancient cave and went inside and sees a ancient coffin with strange words and inside was an ancient Belt he doesn't know what It is but he thinks it's a normal Belt so he puts it on his waist tightly but after he put it on it merge completely inside to his body and feels a little but dizzy and after a while he feels fine but he dreams about a warrior with the same Belt but in an armour fighting monsters and a month later he is accidentally enrolls in Yokai Academy, a school for monsters, and he He befriends Moka Akashiya, a vampire who is drawn to him and navigates his new life amidst other monster girls who develop feelings for him. and he discovered the belt that merge with him can give him an armour and powers but he must learn how to get stronger and learn unlock its full power and Tsukune protects everyone as the warrior.. kamen Rider Kuuga and his life changed forever)

( The Sonic Wave Transformation Belt Arcle (ソニックウェーブ 変身ベルト アークル, Sonikku Wēbu Henshin Beruto Ākuru) is Kamen Rider Kuuga's transformation belt.

An ancient belt created by the Linto Tribe, it is capable of strengthening its wearer and create a biological armor for them to use in combat, but is only usable to those with a righteous heart to prevent abuse of the belt's power. Originally used by the ancient Kuuga, Riku, it was inherited by Yusuke Godai in the year 2000 when he was attacked by Xu·Gmun·Ba, with the belt immediately fused into his body after he put it on.

When he transforms, it reappears around his waist and is always the same color as his current form. A stone embedded in the belt, called Amadam (アマダム, Amadamu), is the source of Kuuga's power and is able to extend the lifespan of a person. The Amadam is also present on Daguva, the Gouram, and Gamio as well.

When Kuuga is imbued with the Golden Power and upgrades into his Rising forms, the Rising Arcle Armor (ライジングアークルアーマー, Raijingu Ākuru Āmā) forms over the Arcle, causing the Amadam to transform into a golden color. When Kuuga transforms into his Ultimate forms, the Rising Arcle Armor upgrades even further into the Ultimate Arcle Armor (アルティメットアークルアーマー, Arutimetto Ākuru Āmā). In this state, the Amadam turns black, while the rectangular tiles that line horizontally across the belt turn silver.

A prototype Arcle was also created, but it lacked the Amadam, which keeps the user from going berserk. Mika Natsume discovered this Arcle and became the second Kuuga in the novel.

When Yusuke asked Sakurako the meaning of the symbols on the Arcle's sides, Sakurako said that it translates to "power".

User Restriction Only the first one to take the belt can become Kamen Rider Kuuga and keep it until the user's death. Which happened with the Ancient Warrior, with Daguva forcing the Arcle out of his body, leaving fatal injuries and leading to his death, before Yusuke wearing it.

Yōkai are a series of supernatural beings that process ranges of power. Yōkai are known to give off an energy field or aura called Yōki. Yōkai monsters ranges from a simplistic monsters like the umbrella like those of Kozo Kasahara to those powerful Shinso Vampire like Alucard. Yōkai monsters have an ability to switch between their monster form and a Human form to hide from the Human population. Yōkai monsters live in a dimensional realm known as the Monster World.

The Gurongi Tribe (グロンギ族, Gurongi Zoku) are a race of creatures who act as the antagonists in Kamen Rider Kuuga.

This mysterious ancient civilization is made up of beings that can transform into monsters to kill people for their ruthless game (ゲーム, Gēmu), which is translated into the Gurongi language as the "Gegel" (ゲゲル, Gegeru). Attacking their rival civilization the Rinto (リント, Rinto), the original Kuuga defeats the leader of the Gurongi and seals all 200 of the Gurongi tribesmen away.

The beings known as the Lords also protected the Rinto tribe. [Citation needed] However, by the present day, the newly resurrected N·Daguva·Zeba revives his tribe from their rest and restart the Gegel on the human race, the descendants of the Rinto, to bring out the "Ultimate Darkness" (究極の闇, Kyūkyoku no Yami), where they commit genocide towards humanity.

They are referred by the Police as Unidentified Lifeforms (also known as "ULFs") (未確認生命体, Mikakunin Seimeitai). Each of them possesses a strange artifact called Geburon on the belt-like (the buckle is called Gedoruto) parts in all of their bodies, no different than Kuuga's Amadam. Gurongi seen in human form are labeled as "B" (Ｂ群, Bīgun), and each human-like Gurongi possesses a tattoo that resembles their true animalistic forms. Unidentified Lifeform #B1 appears in only human form for the entire series outside of a glimpse of her hand or so. Only 48 out of the original 200 Gurongi appeared in the course of Kuuga's broadcast, though some of them were fought offscreen between episodes, and the other 152 were killed off by Daguva after his return for being "unworthy

The Gurongi has a three-part naming scheme that all members have, consisting of "Group-Species-Creature type". The first part of their names indicates their rank and which group that Gurongi belongs to; the second part is their personal name, which contains a reference to what animal/plant their Gurongi forms are based on; and the third part indicates what animal groups they belong to: "Ba" for insects and arachnids; "Da" for mammals; "De" for plants; "Gi" for fish and other aquatics animals; "Gu" for birds and other animals with wings; and "Re" for reptiles and amphibians. The leaders of the Gurongi Tribe will have a "Ze" in front of their animal group names. When talking with each other, they will usually address each other by only their personal names without either group designation. There are four groups shown on screen, namely Xu, Me, Go, and La. Xu, Me, and Go are the only groups allowed to enter the Gegel, while the La Group (namely Balva and Doldo) acts as their judges and the Nu Group crafted their belts and weapons.

A stage show introduces the Be Group as being the lowest-ranking and not allowed to join the Gegel at all. These groups are not permanent, as Me·Galme·Re was promoted up from the Xu Group during the series. Xu is the first group to start the Gegel with Xu·Gmun·Ba as the first player and Xu·Zain·Da as their leader. The Xu Group is assigned a number of humans to kill and tallies them on a Guzepa bracelet. After all the Xu Group were defeated by Kuuga, the Gegel is continued by Me Group led by Me·Garima·Ba and with Me·Vagis·Ba as the first player. Me Group members also use a Guseba but decide their victim number themselves. Later, the Go Group enter the Gegel with Go·Buuro·Gu as the first player and Go·Gadol·Ba as the leader. The Go decide upon a unique pattern for choosing victims, while Doldo tallies their victims for them. Each group has different rules and methods for killing people. The Xu relies on their physical strengths and abilities, such as Xu·Zain·Da using his brute strength to kill truck drivers and Xu·Mevio·Da's immense speed. The Me use built-in weapons such as Me·Geega·Gi's ink bombs, and Me·Vagis·Ba's wrist-mounted stinger gun. The Go Group is the strongest and is able to create weapons from objects they grasp, much like Kuuga. The first player was Go·Buuro·Gu, and their leader is Go·Gadol·Ba, also the leader of the elite Gevagel subgroup of the three most potent Go Group members, who are also capable of changing forms to match Kuuga's.

In the S.I.C. Hero Saga story for Kuuga, it was revealed the Gurongi were once humans, much like the Rinto. They had found a meteorite with strong yet strange crystal-like objects, which allowed to them easily defeat other neighboring tribes and countries by assimilating said crystal into their body and genes of various animals, plants, insects, or fungus that eventually turned them into monsters as they are now.

The etymology of Linto is not certain, but a Korean Kuuga fan blog postulates that it is derived from Japan (Nihon) along with the etymology of Gurongi.

Nihon → Ninho → Rinto.

縄文時代(Jōmon jidai) → ジョグロンジザギ(Joguronjizagi)