This article contributes to the scholarship on digital identity work by examining the linguistic mechanisms of ambient identity construction in fully anonymous online environments. It investigates how video viewers construct textual personae by leaving massive anonymous comments in danmu, a viewing-and-commenting system that synchronously posts comments onto a video screen as it plays. Drawing on the sociological concept of homophily and the linguistics-informed Appraisal framework, this study systematically tracks the patterns in the attitudinal orientations among massive anonymous comments left over a high-profile Chinese video featuring a teacher's home visit. The article argues that the technological affordances of danmu lead to the inherent collectiveness of anonymous digital identity construction. It reports two attitudinal meaning-making mechanisms through which massive anonymous comments converge into a homogeneous mass and describes the viewers' collective ambient identities revealed in their comments. This project brings clarity to the dynamics of ambient digital identity construction by deploying computational tools to linguistic analysis and has practical implications for marketing research, social media monitoring, and community building.