Kousuke Tamura is the younger brother of Yusuke Tamura, the late chairman of Tamura Productions. After Yusuke died in a car accident that also left his wife Minako comatose, Kousuke took control of the company and became the legal guardian of his niece, Eriko Tamura. He manages Tamura Productions with harsh treatment of employees, leading to high turnover, driven by deep-seated resentment and jealousy over his brother's success. This resentment extends to Eriko, prompting him to actively scheme against her growing singing career.

His antagonistic schemes involve financially incentivizing efforts to damage Eriko's reputation, including spreading scandalous tabloid lies. In a significant plot development, he hires men in Guam to physically assault Eriko and destroy a keepsake from her father. All these actions are motivated by his desire to prevent Eriko's success in entertainment.

A crucial familial revelation discloses that established singer Rei Asagiri, who initially resents Eriko, is actually Kousuke's daughter. This discovery adds complexity to his background but does not immediately change his antagonistic behavior towards Eriko.

Kousuke undergoes a reformation towards the series conclusion, transitioning from antagonist to a supportive figure. He assists Minako in regaining control of Tamura Productions and demonstrates care for Eriko, including through comedic scenes involving her dogs. This transformation culminates in his presence at Eriko's performances, where he visibly supports her career.