Surplus incurred from capital transactions of issuing stocks, capital increase, reduction of capital, etc.
Commentary
Capital surplus includes capital excess of par value (amount exceeding the face value), profit from a merger (merger fee - official market price of net assets), gain on capital reduction (face value - payment), and others (government subsidy, grant in aid of construction, insurance gain on fixed assets, gain from assets contributed, waiver of obligation, gain on sales of treasury stock, gain on fixed asset evaluation, etc).
Source
Ministry of SMEs and Startups (Survey on Actual States of SMEs)