This paper examines the relationship between movement-directed affective orientations and youth participation in Spain’s 15M Movement. Drawing on the sociology of emotions and social movement research, the study approaches 15M as a case in which protest participation was associated with a distinctive configuration of positive affective alignment toward the movement. Using microdata from the Spanish Centre for Sociological Research (CIS Study 2,919, n = 1,351 valid cases), a binary logistic regression model is used to assess the association between participation and several affective, political, and institutional variables. The results show that sympathy, hope, enthusiasm, trust, and interest toward 15M are significantly associated with participation among respondents aged 15–29, even when ideological self-placement, political interest, education, democratic dissatisfaction, and institutional trust are included in the model. Negative or distancing orientations such as mistrust, boredom, irritation, antipathy, and indifference do not add comparable explanatory value in the final specification. The article argues that the contribution of the case lies in identifying how a movement born from grievance and institutional disaffection also generated a positive affective structure linked to youth involvement. The findings support an associational interpretation and invite further research on the temporal sequence between grievance, affective identification, and sustained participation in social movements.