Tomohiro Miyajima is the main protagonist of Kaidan to Odorou, Soshite Anata wa Kaidan de Odoru. He and his friends create a fake curse called Ohone-sama for fun which winds up spiraling out of control when they're asked to curse Miyoko Tanashi.
Tomohiro is somewhat smart however he's a little naive.
Tomohiro and his friends Tooru and Hiroyuki break into the donation box at a shrine and, to curb their boredom and make some money, decide to make a curse called Ohone-sama, hoping that people will donate the the shrine. At school they begin scrawling the kanji for "bone" all over blackboards and hiding pig bones wherever they can for students to find. The rumor of Ohone-sama's curse starts spreading around the school, and money starts coming into the donation box.
Tomohiro and his friends later find in the box 50,000 yen and a letter asking them to curse Miyoko Tanashi. That night Tomohiro's aunt Yuka tells him that the police have been getting many reports surrounding Ohone-sama's curse but aren't planning to investigate.
The next day Miyoko discovers several bones inside of her bag even though nobody had been near it that morning. Tomohiro chose not to get involved and figures another student is using Ohone-sama's curse to get revenge on her. He later hears that Miyoko has fallen off of a flight of stairs in the outside prefab building and fell unconscious, and the students are blaming it on Ohone-sama's curse. Tomohiro realizes that he and his friends will probably be tied back to it if the police investigates.
They decide to find out the culprit behind Miyoko's accident and want to check the letter for fingerprints, however nobody has it on them. They then interrogate Rie Satou, a girl who was on bad terms with Miyoko. After a round of bluffing, Tomohiro tricks Satou into revealing that she was on the roof of the school during the accident and could see who pushed Miyoko: she seemed to jump off by herself, as if someone invisible pushed her.
Tomohiro struggles to sleep that night and wakes up to hear Yuka on the phone, learning that Miyoko has woken up and accused Satou of pushing her off. Satou seems to disappear from school the next day as Miyoko returns, with Tomohiro wondering if Satou really lied to him. He heads to the shrine to find the donation box burned up, which likely destroyed the letter as well. Yuka then shows up and reveals to him that Satou was placed under house arrest, as they discovered she was having an affair with a teacher. Tomohiro then realizes that Miyoko was the one who sent the letter in the first place, an elaborate plan to get revenge on Satou for stealing her boyfriend and on a teacher who dumped Miyoko for Satou.
Tomohiro confronts Miyoko about this the next day, and she begins calling him "father" while thanking him for allowing her to become a curse and live on in the school. Miyoko attempts to jump off the roof and Tomohiro catches her, stopping her from falling unconscious like she did the other day. Miyoko then caresses his face and asks if he'll acknowledge her should she continue to be a curse.