The police found 27-year-old Tomohiro Iwazaki near the Tokyo concert venue with a bloody, seven-centimetre-long folding knife close by.

Iwazaki admitted he had lost his temper. He'd sent a gift to pop star Mayu Tomita, 20, which she refused.

Tomohiro Iwazaki, the suspect arrested for stabbing the Japanese pop star. Credit:AP

So, Iwazaki said to the officials, he attacked her.

"I sent a gift (to Tomita) but it was returned," Iwazaki told the police, according to the South China Morning Post. "I asked her why but she gave an evasive answer, so I became mad and stabbed her numerous times."