Kijima started out his career as a Zodiarts Switcher by chance, when he found a Zodiarts Switch that Libra had dropped during a fight with Kamen Rider Fourze and becomes the Pegasus Zodiarts with a new-found taste for power. Using his new found power, Kijima seeks revenge, while also for fun, on the new 2-B homeroom teacher Ms. Haruka Utsugi for taking his rakugo fan by attacking any martial artists he finds, mimicking her fighting style so the Kamen Rider Club would believe she is the Switcher. However, the club learns the truth before Kamen Rider Fourze Magnet States destroys the Pegasus Zodiarts. However, with the Virgo Zodiarts's help when his Zodiarts form resurrects, Kijima is able to evolve into the Cancer Zodiarts, who is armed with a sharp and heavy pincer on his left forearm, capable of cutting just about anything, liquify himself for retreat or disappear, and his body is protected by a hard and spiky carapace strong enough to withstand even the Rider Super Electromagnetic Bomber Limit Break of Kamen Rider Fourze's Magnet States unscathed. All the above combat-specific features, along with the ability to remove the life force of people and place them in comas, enable him to become the most powerful Horoscopes warrior so far.
Although being the latest and youngest member of the Horoscopes so far, Kijima is shown to retain his playful yet arrogant personality and a sharp tongue, as well as insisting to be treated as an equal instead of a trainee. Unlike his other Horoscope comrades, he flaunts his strength without any discretion at all and cares little about his identity being exposed. He also constantly picks fights for fun with Fourze at every chance he gets and manages to overpower him every time, only forced to retreat every time due to various unforeseen circumstances, like Kamen Rider Fourze managing to learn how to immobilize him and proceed to toast him with Fire States' powers. Furthermore, openly rejecting Hayami's offer to learn from him and belittling his contributions, Kijima started a bitter rivalry with the principal as he acts on his own whim with Gamou's approval.
While learning Kamen Rider Meteor's identity, proceeding to mess with him for his amusement, Kijima somehow manages to evoke the latent Supernova powers of the Cancer Zodiarts on his own, enabling him to transform into the more crab-like Cancer Nova, with an even more impregnable armor than his Cancer Zodiarts form. This amuses Gamou even more, although the chairman does muse behind Kijima's back that the Cancer Zodiarts's evolution is going too fast.
After being defeated in his Supernova form by Kamen Rider Meteor's newly obtained Meteor Storm form, Kijima limps onto the AGHS campus and drops his Zodiarts Switch, which Principal Hayami takes. Though Kijima pleads with the principal, saying that he knows with the true identity of Kamen Rider Meteor and the information would prove useful enough to win back Gamou's favor, Hayami dismisses him and decides to do away with him. Finding himself in the form of a meddling detective by Hayami's illusion, Kijima is sent to the Dark Nebula by an unsuspecting Virgo Zodiarts after Hayami talks "her" into it. From there, Hayami covered his trail by claiming that Meteor destroyed Kijima. It is later revealed that, like other persons sent the Dark Nebula by Virgo Zodiarts, he was sent in a suspend animation in the M-BUS.
When first met, Natsuji appeared to be a very jovial person that loved making puns on the fly in a fashion of that of a story, which is to be expected from a rakugo club leader. While he is still this, what he hides behind that is a cold personality that has no empathy for others. He also can be deceptive, as he had lead the Kamen Rider Club around the bush a few times when he was the Pegasus Zodiarts to incriminate Ms. Haruka Utsugi. Despite just joining the ranks of the Horoscopes, Natsuji refuses help from Kouhei Hayami and demands to be seen as an equal and not a junior, starting a rivalry between them.
- Pegasus Zodiarts: he had impressive physical attacking skills, as he mirrored Haruka Utsugi's kickboxing style. Because of this, he was able to fight back Meteor and Fourze on even grounds. However, he wasn't good enough to beat someone like the Libra Zodiarts. Later, he was able to send horseshoe-like pulses of energy by doing Utsugi's signature kick.
- Cancer Zodiarts: Pegasus Zodiarts evolve into Cancer Zodiarts, his skin became protected by a hard spiked shell and became armed with a sharp pincer-like claw on his left forearm, which is sharp enough to even cleave through Fourze's Shield Module, which is made of the ultra-durable metal Astronium, as well as though fire and the environment far in front of him with one swing. His armor can even withstand the power of Fourze's Magnet States; in fact, the beams of electromagnetism were easily deflected in Fourze's first fight with the Cancer Zodiarts. He can also shoot foam from his mouth to serve as both an offensive move or to cover his tracks as he flees. His most dangerous ability is to take a person's souls and make them into rings that when cut has the victim fall into a coma that can only be reversed when someone manages to make him laugh.
However, this powerful Horoscopes has a weakness that he shares with real-like crustaceans: if his claw gets tangled, he can't use it, and thus, can be left open for attacks. He is also weak to prolonged exposure to fire. Also, in his first usage of Supernova, he didn't last long in it, as his body was not yet used to it. Also, his armor was useless to save him from the Meteor Storm Punisher, which effortlessly sliced through his armor.
- Eventually, he gains the ability to become his Supernova form, the Cancer Nova. Unlike the others however, he achieved this state on his own without Gamou and his armor becomes more dense than his Cancer Zodiarts form.