By Makiko Yamazaki and Sam Nussey
TOKYO (Reuters) - Toshiba Corp's ownership restructuring plan faces a challenge, with activist investor Yoshiaki Murakami building a stake in a unit that the conglomerate aims to buy out, potentially making it sweeten an offer.
Toshiba announced last month it plans to take full ownership of chip-making equipment maker NuFlare Technology and two other units through tender offers at a total cost of about 200 billion yuan ($1.84 billion).
Regulatory filings show that funds backed by Murakami, Japan's most prominent activist shareholder, have built a 6.2% stake in NuFlare since Toshiba announced the tender offer for it on Nov. 13.
Toshiba, which already owns 52.4% of NuFlare, has offered 11,900 yen for each NuFlare share. While NuFlare's board has endorsed the offer, Toshiba Machine, NuFlare's second largest shareholder with a 15.8% stake, has yet to decide whether to tender, holding the key to the success of Toshiba's buyout.
Murakami-backed funds also own a total of 9.2% of Toshiba Machine making them the largest shareholder of the former Toshiba unit. Toshiba holds just 2% of Toshiba Machine, having sold the bulk of its stake during a management crisis in 2017.
Murakami could push Toshiba to bump up its tender offer, which ends Dec. 25, or to pressure Toshiba Machine to use its windfall from the deal, said Travis Lundy, an independent analyst who writes on the Smartkarma platform.
The Murakami funds declined to comment on NuFlare. They have not publicly commented on whether they plan to ask Toshiba to sweeten its offer.
A Toshiba spokeswoman said the company is closely monitoring the situation but has no plans to change its offer.
A spokesman for Toshiba Machine said the company is in talks with Toshiba on NuFlare, but nothing has been decided. He also said the company has regular dialogue with investors, but cannot comment on communications with specific investors.
Activist shareholder activity is rising in Japan, with overseas investors sitting on Toshiba's board following accounting scandals and a management crisis at the conglomerate.
Toshiba's bid to buy the units is a major step to moving on from the crisis, as it aims to reallocate resources to focus on growth drivers.
A former bureaucrat, Murakami famously led a fund targeting Japanese companies and pushing for greater shareholder returns until he was convicted of insider trading in 2007. He has since resurfaced as an investor, working with his daughter.
($1 = 108.6400 yen)
(Reporting by Makiko Yamazaki and Sam Nussey; Additional reporting by Junko Fujita; Editing by Muralikumar Anantharaman)