Online video watching coupled with audience interaction through comments overlaid on the video screen is becoming increasingly popular in China. By incorporating features of social media into the design, the underlying Danmaku technology enables users to post comments while viewing videos. The comments are then projected as scrolling titles onto the video screen, invoking a lively and playful viewing experience. Little is yet known about the unique nature of the technology and its attraction, despite growing scholarly and practical interest in Danmaku technology. In this paper, we investigate user experiences to understand the nature and impact of Danmaku technology. We report on a focus group discussion with experienced users of Danmaku video sites. Our findings suggest that the Danmaku functions (interface design, control, augmented display, anonymity) and Danmaku comments (density, relevance, timeliness, subdivision) play essential roles in creating a play experience (company, fun, emotional release, sense of belonging, attentiveness). Design principles and possible applications of Danmaku technology are discussed.