People tend to perceive themselves in a positive light. Typically, they believe themselves to be better than average in accordance with the better-than-average effect (BTAE). The BTAE has been examined with respect to social values (morality and competence) and motivations (self-enhancement and self-protection). Moreover, “competence BTAE” was found to be associated with personality traits while “moral BTAE” was not. However, it is not known whether the BTAE in four domains correlate with certain psycho-behavioral characteristics, particularly moral BTAE. In this study, we recruited 667 Japanese participants (302 males; mean age = 25.80 ± 2.80 years) to assess self- and average other-evaluations in four domains. Self-enhancement and self-protective motives were examined using positive and negative adjectives. We further explored the relationship between BTAE and 22 psycho-behavioral characteristics. The results revealed that moral BTAE only existed in the presence of the self-protection motive. A worse-than-average effect was found in the context of both motives for competence. In contrast to the BTAE in the other three domains, which showed correlations with various characteristics, “negative moral BTAE” was not associated with any psycho-behavioral characteristic. Our results demonstrated that moral BTAE existed only in the presence of the self-protection motive and was “uniquely prevalent”, i.e., was not associated with any psycho-behavioral characteristics. Thus, the psychological mechanisms underlying the negative moral BTAE may differ from the other three domains, potentially reflecting different sociocultural dynamics.