According to local media reports, police have confirmed 27-year-old Tomohiro Iwazaki confessed to the crime at the scene, and was arrested after witnesses said he attacked the star.
A restaurant owner in the building said a trail of blood and a bloodstained mask were found on the stairs leading to the concert room.
The Japan Times reports Tomita was scheduled to perform at the event before she was attacked, in a building near Musashi-Koganei Station in western Toyko.
The Metropolitan Police Department said Ms Tomita had told them earlier that month that a man had been stalking her.
She got in touch with police after he was sending her persistent messages via Twitter, and through her blog.
According to police quotes, he lashed out at her after she returned a gift he had sent her earlier, with no explanation.
“I ambushed her at the station and asked her (about the gift). I lost my temper and stabbed her many times because she didn’t clearly answer,” Iwakazi was quoted as saying.
This is not a lone incident. In 2014, two teenage members of the Japanese girl group AKB48 were attacked by a 24-year-old man wielding a saw, prompting the group to cancel its fan meet-and-greet event.
The suspect was given a sentence of six years in prison.
We all like to idealize and want to live like pop stars because we think thier lives are perfect, this horrible ordeal says otherwise.