"That's how to stop the calamity. How you interpret this is up to you. Just make sure to carefully consider your actions. Think it through, and discuss it with your friends...so you'll have no regrets."

- Naoya Teshigawara

Naoya Teshigawara is a student of Class 3-3 in 1998. He is more often than not the show's comic relief, due to his easy-going nature. He is one of Kōichi Sakakibara's best friends and seems to have a crush on Izumi Akazawa.

Naoya is a young man with light brown hair (which is longer in the manga) and light brown eyes, and he shows a cheerful expression most of the time, yet can be serious if he needs to.

He wears a blue sweater and a white T-shirt, unlike the others who wear their school's uniform. He usually wears a colorful shirt or a flowerish one (for summer) for his casual clothes, which Kōichi Sakakibara considered embarrassing. In "Hair Stand", when he, Kōichi, Reiko Mikami, Izumi Akazawa, Takako Sugiura, and Yūya Mochizuki were going to meet Katsumi Matsunaga, he wore a white and purple shirt and a yellow sun visor.

In the live-action film, he has black eyes and hair.

Naoya is usually superficial in nature. He is shown to have a sympathetic side, since he was the first one to talk to Kōichi Sakakibara, who was still not used to his surroundings. Naoya is very sociable, cheerful, energetic, and is a sports lover. He is a childhood friend of Tomohiko Kazami and a good friend of Yūya Mochizuki, and after Mei Misaki, he is probably Kōichi's closest friend, possibly followed by Yūya.

Naoya is very loyal to his friends. He also seems to be (at least in his mind) a ladies' man, pairing himself with Izumi and Takako for the catching contest (which was his idea in the first place) when the group was at the beach. Naoya is also quick-thinking, immediately springing to the aid of both Junta and Yūya when they were in mortal danger.

Academically, Naoya doesn't learn much at school, claiming that he doesn't know how he reached the 9th grade. He is optimistic and always careless and carefree. However, following Tomohiko Kazami's death, Naoya was riddled with guilt and became more serious and mature as a result.

He is also very selfless and compassionate, regardless of his feelings for Izumi, as well as his fear of her during her run as head of countermeasures, he doesn't hesitate to tell her off when she accuses Mei Misaki of being responsible for the Class 3-3 deaths.

Naoya was the first student to talk to Kōichi on his first day of school, and became his friend soon after. He, along with the rest of the class, was hesitant about explaining the curse to Kōichi, though Naoya promised to explain things to Kōichi in June (which never happened).

In "Put Flesh", Naoya was scolded by Izumi for telling Kōichi unnecessary things about the curse and putting them all in danger, and both of them were arguing when Sanae Mizuno called Kōichi, and overheard her death.

In "Sphere Joint", after witnessing Mr. Kubodera's death, he called Kōichi, Yūya Mochizuki, and Izumi to meet for further discussion of the class 3 calamity.

After learning about Katsumi Matsunaga, they set off in "Hair Stand" to look for him, in the hopes they could replicate his method for halting the curse. During this time, they had fun at the beach while waiting for Matsunaga's return. Naoya organized a competition for lunch. He also picked the teams (pairing himself with the girls, Izumi and Takako), jokingly referring to Kōichi and Mei's team (along with an indignant Yūya) as "the nonexistent team." The results of the game were inconclusive, although Naoya managed to catch a bundle of kelp, which he promptly dropped on Izumi's head.

As the group was preparing to leave, Takako's beach ball blew back into the water. Naoya watched as Junta went to get it and was the first to notice when his classmate stopped moving. Naoya, along with Kōichi and Katsumi, rushed into the water, but were too late to rescue Junta, who was hit by a yacht and eviscerated.

In "Body Paint", Naoya appeared in Kōichi's guilt-driven dream. Later, he met up with Kōichi, Mei, and Yūya to look for the item that Katsumi left in the old classroom. There, they found an old tape recording and began to listen to it. However, they heard a teacher coming and ran to hide, in the process of which Naoya broke the tape. Yūya offered to help fix it, but explained it could take a while.

In "Body Paint", Naoya was among the students who went on the class trip, taking the group picture. By this point, Yūya had repaired the tape, and he, Naoya, and Kōichi listened to the repaired tape and learned how to break the curse: kill the Extra student.

At dinner that night, a tense atmosphere came to a head when Izumi stood up and accused Mei of being responsible for the curse, demanding that she apologize. Naoya took Mei's side and defended her, alongside Kōichi and Yūya.

Shortly after, Naoya barged into Mei's room in order to tell Kōichi he "might have done something terrible." He elaborates in "Makeup", explaining he thought Tomohiko was the dead student. To make sure, he started to interrogate him, and when Tomohiko didn't remember the things they used to do in their childhood, Naoya accused him of being the Extra. Tomohiko denied this, and in their argument, Naoya accidentally pushed Tomohiko out a window. Horrified and sure he'd killed his friend, Naoya had come looking for Kōichi, who assured him a fall from that height probably wouldn't be lethal. However, upon going to check on Tomohiko, they found he was gone.

Naoya later met with Yūya and started to look for Tomohiko, urging everyone to evacuate the building because of a fire. Instead, they met Keiko Numata, who'd already stabbed Manabu Maejima and assaulted Takako in her room, when they went looking for Ms. Mikami, and proceeded to attack them. Her knife falls and cuts Naoya in the leg, preventing him from walking, but Yūya was able to help him escape by dragging him out a window. After Yūya and Naoya escaped from Keiko, he opened an emergency door, only to find her waiting.

In "Stand by Oneself", Naoya was pushed out of a window by Yūya as Keiko continued to chase them. Before Yūya could follow, he was grabbed by Keiko, who tried to pull him back in and finish him. Naoya hurried to the rescue, inadvertently pulling Keiko out of the building and onto him as all three crashed to the ground. Keiko prepared to stab him when Tatsuji Chibiki came in the nick of time and turned her knife on her. Naoya and Yūya followed him to his car, where Mr. Chibiki treated Naoya's leg. A few minutes later, Tomohiko's body was brought out. Naoya screamed at his friend to wake up and broke down in tears upon realizing he was dead.

The anime ends with Naoya and Yūya putting a tape they recorded into the locker, just like where they found Katsumi's original one. Naoya's last lines of dialogue (from the tape) are instructions to Class 3-3, telling them how to break the curse but advising them to work things out as a group, "so you'll have no regrets."

Naoya finds Mei weird and tells her this (to which she calmly responds that he's an idiot). Despite this, they are on good terms. Teshigawara takes Mei's side in "Glass Eye", defending her when Izumi blames her for the numerous deaths. He also enjoys teasing Kōichi about her, often suggesting the two are dating.

Naoya was the first one to talk with Kōichi on his first day at Yomiyama Middle School. They are on good terms, and Naoya often calls Kōichi "Sakaki." He apologizes for the fact that he is obligated to ignore him when he became a non-existent person, commenting that he was lonely without Kōichi to talk to. When Kōichi collapsed due to his lung problems in the manga, Naoya and Takeru Mizuno helped him back to his room. In the same scene in the anime, he took Kōichi's side against Izumi when the latter tried to blame the year's deaths on Mei.

He enjoys teasing Kōichi about Mei, constantly harassing him about being on dates with her.

Naoya is known to have a crush on Izumi, such as in "Hair Stand," when he attempted to get her to sit by him for the trip to the beach. However, she doesn't return his feelings for her as she thinks he's annoying; furthermore, she finds his constant meddling in countermeasures irritating and sees them as exacerbating the problem.

In all iterations of the story, however, Naoya doesn't allow his feelings to dictate his actions, as he stood up to Izumi when she blamed Mei for the deaths caused by the curse. The two don't have many scenes thereafter, suggesting this may have irreparably damaged his chances with her, at least in the anime and novel.

In the manga, however, he went to visit Izumi in the hospital following the catastrophe at the inn, and is there to greet Izumi after she awakens. He notices that she cut her hair and blushes, complimenting her on her new style, before she explained she'd cut it off after the fire. This scene suggests that this universe's Naoya and Izumi are on friendly terms in the end.

This relationship isn't present in the film. Naoya and Izumi never really interacted; however, while trying to escape the Inn with Mei, Naoya took it upon himself to warn Izumi and Takako about the Curse. Instead, he found Izumi standing over Takako, having just stabbed her in the throat. Shocked, Naoya demanded an explanation, but Tomohiko, who was also present, interrupted, revealing he'd seen Naoya attack Yūya and apparently kill him. Panicking, Naoya fled out the girls' window, only to become caught in a live electrical cable and killed. Though momentarily horrified, Izumi realized Naoya's death was a result of the Calamity, and therefore, attacking Takako hadn't solved anything. Since Tomohiko was already present, Izumi decided Mei was the Extra and attacked her next.

Yūya seems to be Naoya's best friend. Whenever meetings are arranged, they always show up together. In "Stand By Oneself", he helped an injured Naoya escape from Keiko. Naoya returned the favor, pulling Yūya through the window, saving his life when Keiko grabbed him.

Tomohiko is Naoya's childhood friend. They also seem to be on good terms, sharing a room on the class trip, and Naoya often teases Tomohiko about his academic prowess. In the original novel, their relationship is more developed as Tomohiko had a larger role.

In the Anime, Naoya noticed Tomohiko couldn't clearly remember some of their shared childhood memories, and assumed that Tomohiko was the other. The two argued, and Naoya pushed him out a window, apparently killing him (Tomohiko actually survived, only to be killed by Izumi when he attempted to kill Kōichi later on). Naoya was horrified by what he thought he'd done, and devastated when he learned Tomohiko really had died.

His epilogue to other students of Class 3-3, about discussing the tape with one's friends rather than acting alone, is likely a reference to his own guilt over Tomohiko's death, suggesting he will carry the weight of his actions for the rest of his life. From the point Naoya attacked Tomohiko on, he was much more serious and darker, as the gravity of his actions caught up with him.

In the manga, Naoya and Kōichi managed to locate Tomohiko before he came to. Kōichi left Tomohiko in the care of Naoya and Yuuya while he went to find Mei. Because of this, Tomohiko survived the calamity and was last seen at the hospital with his friends, checking on Izumi and the other survivors.

In the film, Naoya and Tomohiko aren't especially close. Tomohiko warns Naoya not to do anything stupid when the former starts to suspect Yūya of being the extra, but Naoya ignores the advice. Tomohiko sees Naoya attack his friend and assumes Yūya is dead, angrily confronting him about it when Naoya was trying to escape the inn with Mei. Naoya panicked and fled, only to be electrocuted, revealing to Izumi that the curse hadn't ended.

Although they don't interact as much, it's shown that Aya and Naoya were on good terms. Both were present when welcoming Kōichi to Class 3, with both saying how Yomiyama is a pretty boring place. In Episode 2, Aya is shown to be the only one who pays attention when Naoya explains his Apple drawing in Art class to Ms. Mikami. She also calls him "Teshy", one of the many nicknames she gives her friends. Naoya was the one who asked if she and Yumi Ogura would want to search the old school building with him and Kōichi, which she and Yumi decided to pass on. After she leaves, it's the last time Naoya ever sees her. Naoya probably found out about her death later and was saddened, with the rest of the class offscreen.