Individual success stories aside, experts and executives agree Japan needs more dynamic, risk-taking business chiefs.
"There are huge numbers of people working at companies who have never seen their firm grow in the years since they got their jobs," said Gree's Tanaka, who himself got a taste of start-up success when he worked at Rakuten - and whose offices occupy the same Roppongi Hills complex that was home to a once high-flying Internet entrepreneur, Takafumi Horie.
"So even if you tell them that growth and success are interesting or fantastic ... it doesn't seem real."
Aggressive self-starters also remain a minority in part because those who succeed too well risk a social backlash.
"Japanese who become truly successful are often pulled down by society for that very fact. It's the cost of jealousy," said Akira Sato, a partner in Japanese consultancy Value Create.
Gree's stellar profits may be one reason the firm has attracted criticism from media for the big bills run up by minors buying virtual accessories to improve their scores, Waseda's Negoro said. Last month, Gree announced it was capping the amount under-20s could spend.
"Japanese don't like it if someone makes too much money. You should make just enough," Negoro said. "That's the Japanese tradition."
Rakuten's Mikitani, though, thinks the chill in Japan's appetite for entrepreneurship that followed Horie's 2006 arrest and subsequent prison sentence for accounting fraud is thawing.
Horie's aggressive takeover battles and high-flying lifestyle rattled corporate Japan, and many felt his 30-month prison sentence reflected an establishment backlash.
"We are feeling that young people are being a little more ambitious and the trend is turning back again," Mikitani said.
On-line organic food grocer Oisix's Takashima says opportunities abound for the ambitious, though he adds he wants to make the world a better place, not just rake in profits.
"Japan is the world's third biggest market, is very attractive and is being ignored," Takashima said. "There isn't much competition, so I have a lot of freedom. It's a great environment. I'd like to keep that a secret.
($1 = 82.2950 Japanese yen)
(Additional reporting by Reiji Murai and Ritsuko Shimizu; Editing by Ian Geoghegan)
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