TOKYO, May 20 (Reuters) - Activist investor Oasis Management on Monday said Japanese paper manufacturer Hokuetsu's plans for a strategic alliance with Daio Paper lacked numerical details on where synergies could be gained.

Oasis in a statement called the plan "a transparent attempt by President Kishimoto to yet again overpromise and underdeliver".

The comments follow Oasis' call for the dismissal of CEO Sekio Kishimoto and four independent directors in a shareholder proposal earlier in May.

Hokuetsu announced the alliance last week and said the firm would also divest its cross-shareholding in Daio.

Oasis said Hokuetsu's relationship with Daio had failed to generate synergy in the more than 12 years since Hokuetsu first acquired Daio shares.

Hong Kong-based Oasis said it beneficially owns around 18% of Hokuetsu shares and has been engaging with the company since 2019.

Oasis separately submitted a shareholder proposal last week against the reappointment of the chairman and two directors at Kumagai Gumi, arguing the construction firm's mid-term plan aims to reduce capital efficiency even though it would increase profit.

Oasis also called for an increase in Kumagai Gumi's dividend to bring it in line with peers.

Shareholder activism is becoming more prevalent in Japan as the government and regulators join investors in calling for corporate governance change and improved shareholder value.

In January, the Tokyo Stock Exchange began publishing names of listed companies that have disclosed plans to raise capital efficiency, in effect shaming those that have not.

"Now that we have the form of governance we need the substance of holding managers accountable," Oasis' founder and Chief investment officer, Seth Fischer, said at a press briefing in Tokyo on Monday.

Last month, Oasis launched a campaign targeting cosmetics and skin care company Kao, calling on management to prioritise foreign marketing and streamline its brand portfolio.

Fischer will meet Kao's management in the coming weeks, he said at the briefing. (Reporting by Anton Bridge; Editing by Christopher Cushing)