Yuusuke Godai is a carefree, gentle spirit, always willing to help out people. One day, he has a vision of an artifact called the Arcle, and eventually puts it on after the first of the unsealed Grongi attacks. At first, his white Growing Form is dubbed Unidentified Lifeform No. 2 by the police, and his subsequent forms are dubbed Unidentified Lifeform No. 4. As the police learns of his identity, they begin working with Godai. After seemingly dying at the hands of the mushroom Grongi Me-Ginoga-De, Godai's premonitions combined with Dr Tsubaki's defibrillator awaken a new power in the Amadam, the stone within the Arcle. This unlocks a new level of power, the Rising forms. In his hatred for Go-Jaraji-Da, he channels Ultimate Form, a form powered by anger, as he defeats the Grongi. Eventually, once all the other Grongi are defeated, N-Daguva-Zeba, the Grongi leader, comes and nearly kills Godai, challenging him. Eventually, Godai transforms into Ultimate Form, but firmly under his control, and engages in a brutal battle with Daguva, narrowly winning after both their Amadams were destroyed and reverting into human form.
Adorkable: He's known for having some strange hobbies, most notably archaeology.
Chest Insignia: After a certain point, he starts wearing shirts and jackets marked with Kuuga's emblem.
Comes Great Responsibility: Inversion, With Great Responsibility Comes Great Power. The first time Yuusuke transforms, it's just to save himself, transforming into the weak Growing form. It's in his second battle, with the resolve to protect humanity from Grongi, that he activates the Mighty form.
Cool Bike: The TryChaser 2000 and the BeatChaser 2000.
Dark Is Not Evil: Kuuga's Amazing Mighty and Ultimate Forms are black with gold, and in the final episodes Yusuke wears a lot of black. He's still as heroic as he ever was, though.
Dark Is Evil: But, Ultimate Form is perfectly capable of corrupting Yuusuke, so this applies too.
Destructive Savior: The Rising forms are powerful enough to cause catastrophic explosions; thus Godai and the police work to avoid this by diverting battles to more secluded locations.
Elemental Powers: Downplayed as Kuuga does not actually invoke the elements themselves (unless otherwise stated). Each of the four forms of Kuuga is themed after an element and implied as such based on in-universe translations of the Linto language. Heck, even Godai's own surname is tied to the four elements.
Nice Guy: Probably the ultimate example in Kamen Rider, though later on Eiji would give him a run for his money in this department.
Reluctant Warrior: Hates fighting, but due to the Grongi threat has no choice but to.
Super Senses: Pegasus Form enhances all of Godai's senses. Unfortunately, these hightened sense are so sensitive that he can only maintain Pegasus for about fifty seconds before he suffers Sensory Overload and is forced to change out of it.
Dual Wielding: How you could upgrade a BFS after making it even larger? Use two of them. And thus we have Two Rising Titan Sword used for the Double Rising Calamity Titan attack.
Ichijo is a young police officer from the Nagano police who is assigned to the national police squad dealing with the Unidentified Lifeforms. He uses his influence to eventually help Godai, and eventually the police help Kuuga.
Yusuke's sister, who works at a children's daycare that Yusuke occasionally visits. At first wary of her brother's new powers, Minori became supportive of him. She helps out at the Pore-Pore Tea Cafe whenever hands are short.
Dr Tsubaki is Godai's doctor, treating his various injuries, and taking notes on the Arcle. He also performs autopsies on Grongi victims, and even on the body of Zu-Gooma-Gu, eventually leading to the conclusion that the Grongi work similarly to Kuuga.
The Head of the Police Department Science Division, the single mom is a personable scientist who studies the Grongi and develops weapons against them. Due to her workload, she doesn't have much time to spend with her son.
Friends of Yusuke's father, who looked after him and Minori when their parents passed away. Affectionately called Uncle, he runs the Pore-Pore Tea Cafe and is the series Comic Relief, though they are too outdated or obtuse for anyone to understand. Collects a scrapbook of Kuuga's exploits, though ignorant Yusuke is that hero, initially.
An aspiring actress, she moved in with her Uncle Kazari to take up acting school in Tokyo. She had a crush on Yusuke, and helps out at her Uncle's cafe. Though a lighthearted character, the murder spree of the Grongi occasionally hits close to home.
Jean Michel Sorrel
A transfer student from France, he shares the office with Sakurako and gets gradually roped in the circle of Kuuga. He has revealed that he had once failed a child. Has a crush on Enokida and tries to help her reconnect with her son.
Gratuitous English: Though he supposes to be French, Jean occasionally uses English words and phrases.
The older coworker of Ichijou who is his comrade in the battle against the Grongi. Though initially skeptical of Kuuga, he is saved by the hero and becomes a supporter, to the point he learns his true identity. Has a child that went to Minori's daycare.
A coworker of Ichijou who is his comrade in the battel against the Grongi. Supports Kuuga, , to the point he learns his true identity.
The policewoman part of the Grongi team who runs police dispatch, and becomes one of the people who knows Kuuga's true identity. Has a bit of a crush on Ichijou, who politely doesn't return her feelings.
Daughter of one of the professors murdered by Daguva, she is initially suicidal because her father's killer hasn't been found. She makes up for this by joining Jean's investigation group in Nagano. Once that concludes, she decides to take up the flute.
Yusuki's elementary school teacher, he has a moment of personal crisis when he believes he could no longer teach. Sakurako and Yusuke help him overcome that, and Kanzaki occasionally returns as a recurring character.
A man with a life-threatening disease and troubled lot in life, he was a supporter of the Grongi until Kuuga saved him. He briefly returned, revealing to have a personal crisis after having his entry rejected from an ad contest.
The ruler of the Grongi tribe. He is the first Grongi to be awoken and was the one to revive all 200 of the rest of his tribe (although he slaughtered a large number of them as they were too weak to fight Kuuga). Dubbed Unidentified Life Form 0, Daguba took the form of a young man in white towards the end of the series once Kuuga defeated the Zu, Me and Go tribes. Towards the finale, he attempted to bring about the 'Ultimate Darkness' to turn humans into a violent race like the Grongi. Yuusuke eventually confronted Daguba in the mountains and after cracking each other's belts, were both forced into their human forms where they fought hand-to-hand. In the end, despite dealing Yuusuke a critical blow, Daguba was killed.
The Bat Grongi of the Zu tribe. First appearing in Episode 2, Gooma was disguised as a priest and resided in a church where he preyed on his victims during the night due to his photophobia. After his first battle with Kuuga, Gooma lost the right to continue participating in the Gegeru and was unable to advance in rank. He mostly hung around the Rose-Tattooed Woman looking for any chance to rejoin the game but being shot down each time. Eventually, he discovered pieces of Daguba's body and ingested them to gain a power-up. This allowed him to overcome his photophobia and even provided him enough strength to succesfully square of against Kuuga's Titan form. Eventually, while attempting to usurp Daguba, Gooma was killed by the Grongi leader although his body was eventually used to develop anti-Grongi bullets.Gooma was one of the longest lasting Grongi, surviving the Zu tribe, the Me tribe, and all but the final three members of the Go tribe.
Evil Counterpart: Along with Daguba, both Go-Badaa-Ba and Go-Gadoru-Ba parallel Kuuga in different ways. Badaa, like Kuuga, is a Badass Biker whose animal tattoo just so happens to be the motif of the first Kamen Rider. Gadoru, as the leader of the Go Tribe, is able to change between forms, five in total, each paralleling one of Kuuga's base four forms and his Rising form. It also helps that his animal motif is a rhinoceros-beetle.
Eye Scream: Zu-Mebio-Da is shot in the eye by police, with bloody results.
Transformation Trinket: It's eventually revealed that the belts all Grongi wear function nigh-identically to Kuuga's Arcle, fusing with their nervous systems and giving them the ability to transform into powerful combat forms. They're probably the only Kamen Rider monsters where their true forms are their human forms.
Wicked Cultured: Some of the Go class; one reads the collected works of Camus, while another plays Chopin at the piano.