How does the choice of electoral rules affect politicians' incentives to campaign on the basis of personalized support? This article examines to what extent the adoption of new electoral and campaign finance rules affects the incentive of politicians in Japan's Liberal Democratic Party to rely on personal support organizations called koenkai. The core of the analysis utilizes newly collected campaign finance data. The empirical analyses confirm a considerable weakening in the number of koenkai across systems as well as a decreased need for politicians to spend money in the proportional representation tier. These results highlight the importance of previous organizational legacies as well as the efforts of political actors to mitigate the effects of rule change on their election and reelection prospects.