At first, they blackmailed their victim. Again and again, four high school students sent text messages to their classmate, demanding hundreds of thousands of yen.
Then they posted a nude photograph of the 18-year-old boy online, complete with phone number and email, leading to more text messages on his mobile phone and humiliation.
In the end, the student saw only one solution to end his torment - and jumped to his death from the roof of his school in Kobe, central Japan, in late 2007, a case that shocked the Japanese public.
It is not the only case in Japan where mobile phones, an omnipresent gadget on the high-tech islands, were used for student mobbing, or bullying.
For both offenders and victims the mobile phone is a main communication tool, and they are increasingly regarded a source for many problems, ranging from mobbing of students and teachers; schoolgirls prostituting themselves via the Internet, to suicide guidelines, leading the government to advocate a cellphone ban in Japan's public schools.
According to media reports, the education ministry plans to ask school authorities countrywide to ban mobile phones in primary and secondary schools.
However, critics doubt a government ban will make the problems simply go away.
"Even when I am convinced that a child has a mobile, I cannot simply take it from them. Then I would be accused of using physical punishment," an Osaka schoolteacher said, explaining her dilemma to the Asahi Shimbun newspaper.
According to a poll of 11,000 students by the education board of the Tokyo prefecture, 33.2 percent of 10-year-olds own a mobile phone, or keitai, as it is called in Japanese. The share grows to 73.3 percent by the age of 15 and 95.4 percent of 16-year-olds own a mobile.
A study in Osaka prefecture showed that one out of six 13-year-olds used their phone more than three hours per day, among 16-year-olds, it is one third. Additionally every sixth 16-year-old said they sent more than 50 text messages per day.
It is not surprising that the same study said the more time children spend with their phone, the less they study at home.
In Japan, where mobile phone technology is about three years ahead of Europe, the full-time Internet-access keitai is a fixed part of public life. Long gone are the days when the phone was only used to make calls or send text messages.
Japanese can pay for buses, trains or even taxis, receive free television broadcasts, book holidays, read manga comics or complete novels, just using their mobiles. However, equally on offer are porn, internet sites where people meet up for planning collective suicides and so-called deai saito sites, where adult men can hook up with schoolgirls for sex.
One in 10 primary school students was exposed to such material at least once, a survey said.
The effectiveness remains to be seen of a recent amendment to Japan's Internet laws which orders Internet providers to delete website entries from children under 18 offering sexual services and adults looking for them.
Japan's police said within one month of the amendment, 1,600 contact sites were registered with local public security boards.
When Osaka's young governor, Toru Hashimoto, recently called for a cellphone ban in schools, he caused a stir. Up to now, schools were free to deal with the problem individually. Many issued bans, to little effect.
Communication Minister Kunio Hatoyama welcomed Hashimoto's suggestion, saying that "people heavily dependent on cellphone e-mails would lose conversation capabilities".
"It's no doubt true that mobile phones have an aspect that could lead to a loss of humanity (on the part of their users)," he added.
Yet, there is also opposition to a mobile ban in schools. Nationalist Tokyo Governor Shintaro Ishihara said the decision should be up to the parents, the Kyodo news agency reported. Others stress the positive, saying schools and parents could use phones to locate children, making sure they are safe.
And then there are those like Shigeki Ito of Komazawa University, who points out that a ban at schools would be pretty pointless, as kids would just go on using their mobile gadgets after school.