Hedge fund Aspex Management had urged Nidec to retain chief executive Mitsuya Kishida to help steer the Japanese electric-motor maker through an accounting crisis and potential restructuring, shortly before his unexpected resignation was announced, according to a report by Bloomberg.

Aspex, which says it holds about 7% of Nidec, sent a letter to the company's board on 28 September calling for Kishida to remain in the top job, provided he was deemed suitable to continue. The hedge fund said Nidec needed management continuity as it worked to restore its financial reporting and address a delisting warning from the Tokyo Stock Exchange.

Kishida's departure was announced by Nidec on Tuesday after being reported by a Japanese magazine, contributing to a sharp sell-off in the company's shares. The stock fell 21% through Tuesday amid the leadership change and reports that Nidec could face a new impairment charge of around JPY1tn ($6.4bn).

Aspex also called on Nidec to update its medium-term business plan, arguing that the company needed continuity while pursuing its longer-term objectives.

The hedge fund's letter said it would support Kishida remaining chief executive as long as he continued to meet the required standards for the role. Aspex's intervention came as Nidec prepares to restate some previous financial results and deals with the fallout from accounting irregularities uncovered last year.

Nidec said Kishida had engaged in remarks and actions relating to financial reporting that it considered inappropriate. The company reportedly did not respond to a request for comment on Aspex's letter.

Michio Kaida, Nidec's chief technology officer and a longtime member of the group, has been appointed to replace Kishida with immediate effect.