|Relationships|| Tatsuhiko Kimura (uncle)|
Tomu Shirasagi (love interest)
Yuka Tsukiyono (roommate)
Natsumi has long, pink hair tied in two side tails which usually blow upwards whenever she feels shock or excitement.
Though her outfits changes and does not have an iconic standard outfit, her casual wear often involves short hoodies sporting some short word or acronym that reveals her midriff and belted short jean shorts that reveal her long, slender legs, as well as high-heeled leather boots.
Natsumi is quite bubbly and cheerful, which earned her a fanclub among the students as Shishido Academy's Idol. She is also heavily romantic and open about her feelings towards Tomu.
Natsumi is Tomu's first female supporter, having been attracted to him upon first sight. She attempts to Become his manager to help him out on his quest, which he politely declined. She then attempted to challenge him to a gamble using cards, which Tomu accepted, but had already seen through her trick. Before she could be defeated, her roommate, Yuka, pulled her own cheat at the last second to save her from humiliation. Natsumi returned later to apologize for what had happened, returning all the money lost. She would later serve as Tomu's cheering section when he faced off against Yuka in a game of blackjack. She and Mizuhara quickly took Tomu to the hospital to get his finger reattached and would visit him on their free time.
When Tomu was challenged by Rio to a billiards match, Natsumi introduced Tomu to her Uncle Tatsuhiko, a former pro billiards player, in order to receive training and a place to practice. Her uncle refused, then they are met by Gokujima the Hustler. Tomu managed to con Gokijima with his own philosophy which angered him, by was immediately beat down by Natsumi. Gokijima then coached Tomu in pool and to rig the game in his favor. Natsumi served as the announcing referee for the billiards match between Tomu and Rio. At the last game where Tomu needed to "run out" to win and an incident where the balls had supposedly been moved due to table movement, it seemed the worst thing to happen for To,u as the balls were in a position where he couldn't possibly win, but he did using a trick shot. It was revealed that when the audience was distracted, Tomu, Mizuhara, and Natsumi had rearranged the balls themselves to set up the trick shot win. It also turned out that Natsumi had talked with her Uncle Tatsuhiko beforehand to help with the little "performance" to make it all the more convincing.
In the dice battle, Natsumi volunteered to be one of Tomu's two teammates, but was turned down in favor of Yuka and Megumi since she herself didn't have any sort of special talent that could be helpful. This lead to Natsumi getting angry and slapping Tomu for his supposed insensitivity before storming off. At the time of the dice battle, Yuka was taken out of the running by Megumi, who turned out to be part of the Abidani Seminar, Nana Hiruko. His team now dwindled down to just himself, Natsumi quickly jumps in to fill in a spot where she challenged Nana in "strip dice". Unfortunately, since Nana's ability is to make fast calculations, Natsumi began to lose her clothes fast. Quick thinking allowed her to turn the tables by using a loophole in the calculation rules, so now Nana gets stripped down to next to nothing. Unfortunately, Natsumi loses out in the end. In the judgement fire dice battle with Tomu and Mayo, Tomu requested for Natsumi, Yuka, and Mizuhara to strip off their clothes so that he could use them for cover against a flaming pot.
Natsumi, along with Yuka, Mika, Yoshio, Nana, and Gokijima join Tomu in the flag capture game against Emily Dawn and her commando team up in the snowy mountains north of Shishidou Academy.
She would then accompany Tomu along with Mizuhara and Yuka to Mcau City where the Class Reunion was going to be held. When Tomu gets hospitalized, She, Mizuhara, Yuka, and Rio try to gain 1 billion yen in chips for the entry fee for Tomu. They all imagine how grateful Tomu would be and the extra cash left over, in which Natsumi declares she would use to fund her wedding to him. Natsumi tries her hand at craps, winning big, but then eventually losing it all.