Tokyo stocks posted a series of sharp gains on August 12 as strong earnings, higher shareholder returns and large-shareholding disclosures fueled buying across the market. M3 rose 6.1% to ¥1,631.5 after a filing with the Kanto Local Finance Bureau showed Hong Kong-based Oasis Management held a 5.03% stake, prompting expectations of activist involvement as the fund said it aims to engage management on medium- to long-term corporate value and governance. Seikoh Giken climbed 12.5% to ¥23,700 after raising its consolidated operating profit forecast for the year ending March 2027 to ¥12 billion from ¥8.3 billion and lifting its annual dividend forecast to ¥30 from ¥24, citing stronger demand for optical connectors used in and around AI data centers. Other notable gainers included Taiyo Yuden, which rose 7.5% after disclosures showed Situational Awareness had built a 16.61% stake, and Sinanen Holdings, which hit its daily limit after reporting a 2.5-fold rise in quarterly net profit and announcing a buyback. Soliton Systems, Milbon, Resorttrust, meito, Yonex and Monogatari Corporation also advanced after profit upgrades, stronger results, buybacks or dividend increases, underscoring investor appetite for companies offering earnings momentum and clearer shareholder return policies.