Yajiro Kojima Kuramitsu (great grandfather)
Rushuna Tendo Kuramitsu (great grandmother)
Mikan Kurenai Kuramitsu (great step-mother)
Kanako Urashima (step sister)
Haruka Urashima (aunt)
Hina Urashima (grandmother)
Self-described as plain-looking and un-cute, Keitaro Urashima is an uninteresting guy and a failure as a second-year Ronin.
Keitaro was in the 48th percentile, bad at English, Math, Social Studies, History, Biology and Sports. However, his reliance and dedication to his dreams and the memory of a promise drives him to continue pursuing the near-impossible task of entering Tokyo University; one of, if not the, most prestigious university in Japan.
Honest and hard-working, Keitaro’s empathy towards other people and their problems, coupled with a desire and compulsion to help, sometimes causes him to become involved in things he shouldn’t be or become entangled in elaborate adventures that cause him to digress from his studies.
Keitaro was born with a power to that point unknown to the Kuramitsu though Yojiro suspects that it might simply be a ki-process. While the majority of it is still sleeping a by product of it makes him nigh indestructible able to survive large amounts of damage that most people would possibly be killed by. Naru mentioned he was cute without his glasses.
Kicked out of his home for his continued persistence to get into Tokyo University and promising that he would not return until he entered Tokyo U, Keitaro makes his way to the Hinata Apartments to stay, however he soon discovers that it has become an all-girls dormitory. Mistaken for a Tokyo University student Keitaro is allowed to stay despite mistrust from the girls, particularly from Naru Narusegawa, who was also studying for Tokyo University. While it is eventually discovered that he was not a student of the university, Keitaro receives a fax from Grandma Hina Urashima and becomes the landlord of Hinata House.
While studying for the entrance exams and attending to landlord duties, Keitaro manages to gain Naru as a study accomplice and tutor. While accidentally peeping in her diary, Keitaro begins to suspect that Naru was his promise girl. While failing his mock entrance exam and experiencing a bad luck prediction during the New Year’s festival, Keitaro’s relationship with the residents of Hinata House, and Naru in particular, began to improve; with Keitaro receiving his first Valentine’s Day chocolates from the girls. However, in spite of this, when Keitaro learned that the promise that he had read in Naru’s diary was not to him but to her old tutor on the eve of the entrance exams, his distraction was such that he ended up failing the exam.
Deciding to take a trip of healing through southern Japan, Keitaro ends up repeatedly running into Naru, who had also failed the exam and was following the same travel route as Keitaro. Opting to travel together, they run into Mutsumi Otohime while on a cruise to Kagoshima. Discovering that she, also, was on a trip of healing after having failed her Tokyo University entrance exam and concerned over her anemia, the pair include her in their travel group to see her home to Okinawa. During the trip Keitaro and Mutsumi exhibit uncanny similarities and discover many similar interests, so much so that Naru begins getting jealous over their compatibility.
Following their return to Hinata House, Keitaro begins looking for a job to restock his savings after the trip, however in the process he learns more about Naru’s promise and crush with her tutor. Eventually getting a job as an item mover for Noriyasu Seta, Keitaro becomes his assistant after demonstrating his ability to babysit Seta’s charge, Sarah McDougal, however, when it is discovered that Seta was actually her tutor and the two are reacquainted, Keitaro helps Naru make her feelings known to Seta puts his feelings for her aside.
Attempting to avoid her, even when the Hinata residents are employed by Haruka to work at the Hinata Seaside Teahouse, the pair’s relationship becomes strained after a misunderstanding caused by Haitani and Shirai’s meddling however after Keitaro makes a stand against Seta during a play rendition of Journey to the West and Naru and Keitaro become stranded on an island thanks to Sarah’s antics their relationship begins to heal to the point that Naru and Keitaro go on a date through Hinata.
When Mutsumi arrives at Hinata to attend the coming Tokyo University Entrance Exams Keitaro becomes turn between which girl to pursue, and matters are complicated more when Naru discovers that Mutsumi might be the promise girl Keitaro had pursuing these past years. Similar to how Keitaro performed when Seta arrived, Naru begins encouraging Keitaro and Mutsumi’s relationship in spite of Keitaro being undecided on who to choose.
While managing to pass his coming exams even while becoming freaked out and getting asked out on a date by Mutsumi, Keitaro’s confidence soars after it is cleared that Mutsumi’s promise was made not to Keitaro but to Naru; clearing her of being Keitaro’s promise girl. However he daydreams during the entrance exam and becomes convinced that, as he had rushed to complete it before the time ran out, he had failed the exam again. Not wishing to confront his friends and bare their disappointment he boards a boat heading overseas, however he falls overboard mid-voyage and ends up stranded on a tropical island called Pararakelse. Meeting Seta on the island, Keitaro volunteers to work as a hired hand in his excavations of the island.
Chasing after him, Naru joins Keitaro in the excavations; ending up getting lost in the island’s desert in search of the Turtle Civilization. When the rest of the Hinata residents also pursue after them after learning that they had both passed their Tokyo University entrance exams Keitaro manages to send his entry ticket to the university on time to finally become a Tokyo U student. On the first day of attending the university, Keitaro suffers a broken leg when a roof ornament falls on him. Forced to take a leave of absence he admits his love to Naru while in hospital.
Following his return to the apartments he attempts to receive a response from Naru only to have her avoiding the subject in spite of Mitsune’s well-meaning meddling. When Motoko’s sister makes a proposition that Motoko either best her in combat or marry Keitaro; whom Motoko had lied about being her fiancé, and healing and witnessing Seta and Haruka’s own ponderous relationship, Naru finally reveals her conflicted feelings to Keitaro.
While traveling to Okinawa with Mutsumi to visit her family, Keitaro and Naru end up having to look after her when she loses her memory and regresses to her childhood, reliving the circumstances surrounding his childhood promise.
Returning back to Hinata, the group came across Yajiro Kojima Kuramitsu, Rushuna Tendo Kuramitsu, Mikan Kurenai Kuramitsu who claimed to be the original owners of the land when Naru demanded to know who they were. Despite Kanako attempting to defend him Keitaro was instantly placed into the Family Love Glomp by Rushuna upon introducing as Hina’s grandchild when Yajiro asked where she was.
They were interrupted by Hina rushing into the dorm only to stop upon seeing what was going on. With nothing left to do Hinata revealed her true form to her family and explained what was going on. Keitaro was shocked by the revelation that not only was his grandmother an alien but had set him up to be engaged with all the girls of the Hinata House. He was also surprised that his grandfather wasn’t aware of this fact. Though this was the one question Hina readily had an answer for explaining that her husband thrived as a human and thus chose to die as a human.
After such an eventful morning Keitaro decided to take a bath as he struggled to understand all the changes in his life. Finding his grandfather already soaking in the barrel he joined him at the man’s insistence as he wanted to discuss the day’s events with his grandson. Yajiro soothed one of Keitaro’s fears that he didn’t have to leave the planet and could continue his education though he would have to eventually if he and the girls decide to get the medical upgrades that extend their lives.