When creators post their content to pixiv's services, it is evaluated (for impressions, hype, degree of influence, etc) and rewards are given by pixiv as compensation. You can start receiving rewards by agreeing to the "Rules on the Receipt of Rewards" and turning on shoutouts when you stream. Every month, pixiv will evaluate your contributions based on information like the number of clicks generated and the number of reactions received to decide on the amount of the reward.