Nidec's accounting issues include improper bookkeeping at subsidiaries and within its automotive electric-motor inverter business, leading to expected ¥250 billion in impairment charges. Nidec Corp. shares rose the most in a week after Oasis Management Co. disclosed a sizable stake in the electric-motor manufacturer, calling for sweeping governance reforms after its accounting scandal. The stock jumped as much as 7.9% in early morning trading on Thursday in Tokyo. Oasis revealed it owns 6.74% of the Japanese company, which is in turmoil following cases of improper bookkeeping at subsidiaries in Italy, Switzerland and China, as well as within its automotive electric-motor inverter business. That saw the company brace for ¥250 billion ($1.6 billion) in impairment charges and forced founder Shigenobu Nagamori to resign as it faces the risk of becoming delisted from the stock market. Oasis said the company has potential and its stock is undervalued, but it needs an overhaul to regain the trust of the market. Nidec's improprieties are "extremely serious," Oasis said in a statement Wednesday, adding that the issues "are not merely isolated incidents, but rather, structural problems arising within a corporate culture shaped by excessive pressure to meet performance targets and the strong influence of the company's founder." Earlier this month, Nidec announced several executive departures and warned there could be additional charges that impact past financial results. Investigators said in preliminary findings that they had uncovered at least a thousand instances of improper accounting. The irregularities first surfaced last year. The issues inflated values of raw materials and inventories, incorrectly declared customs values, government grants presented as revenue in financial statements, and labor costs counted as fixed assets to defer expenses. As financial pressure built, units attempted to cover losses by reporting higher revenue but in turn that led to even greater strain. Nagamori, whose unrelenting performance targets were blamed as a root cause of the whole ordeal, gave up his position as chairman emeritus last month. He had left the board in December, though he remains Nidec's largest individual shareholder.