A full understanding of directors’ fiduciary duties toward shareholders requires clarification of their shareholder-protection function in capital transactions, which constitute the very subject of regulation. This study, building upon the frameworks of the "identity theory," "difference theory," and the debates on "inclusion versus exclusion," analyzes the liability of directors of a subsidiary toward each shareholder in cases involving the issuance of new shares and mergers, particularly in the boundary case where the shareholder is a parent company, i.e., a "corporate shareholder." The analysis suggests that the recent amendment, in its interpretative formulation, lacks sufficient instrumental adequacy due to its abstract and comprehensive nature. To address this deficiency, the study proposes a legislative reform introducing Article 382-5 of the Korean Commercial Act, explicitly codifying directors’ "duty to transfer fair value." However, the research does not extend to issues concerning the future direction of legislative reform on merger ratios among affiliated companies under the Financial Investment Services and Capital Markets Act, nor to cases involving corporate shareholders in spin-offs, reverse stock splits, or other capital transactions. These matters remain for future research.