Idemitsu this month launched a public tender offer to buy all of the shares in Toa Oil for 15 billion yen ($145 million). Idemitsu, which already owns 50.12% of Toa, aims at least to acquire a further 16.55% stake to succeed in the bid.

The move comes as tender offers in Japan face increasing obstacles, with investors seeking higher offer prices and the government pushing for better shareholder returns.

Toa Oil shares closed at 2,542 yen on Friday, above Idemitsu's 2,450 yen offer price.

Cornwall Capital said in the filing that it invested in Toa to manage its clients assets, but it could hold constructive and friendly discussions with the company management.

The U.S. investor has been gradually building its stake in Toa since 2018, according to filings the fund has made.

($1 = 103.4800 yen)

(Reporting by Junko Fujita; Editing by William Mallard)