Collective rituals, particularly those characterized by synchrony and pain, have been shown to yield positive social and emotional outcomes. The question arises as to whether these findings extend to low-arousal, family-centered rituals and how spiritual beliefs factor into these communal practices. This study set out to examine the interplay between belief, ritual participation, and their effects on anxiety, social cohesion, and prosocial behavior during a low-arousal collective ritual in Mikasa, Japan. Drawing upon a sample of 183 festival participants, we measured belief in ancestors using a novel scale, identifying significant and consistent associations between these beliefs and measures of social cohesion across multiple targets. Moreover, active participation as a festival dancer displayed a positive relationship with feelings of social cohesion, particularly towards other festival attendees and at the national level. On measures of prosocial behavior, ancestral beliefs were positively associated with generosity shown within the festival setting, whereas observers were less generous towards community members than a non-attending control group. Anxiety outcomes displayed a negative relationship with ancestral beliefs and ritual observation but not participation as seen in previous research, suggesting a complex interplay between rituals, emotions, and individual states. These findings provide novel insights into the importance of belief systems and active participation in shaping social bonds and behaviors in the context of collective rituals.