Background: Very few studies have examined the relationship between stress and the extent of suicide attempts in patients with transdiagnostic mental disorders. We examined the relationship between suicide attempts and stress-related indicators such as stressors, character traits, and coping strategies. Methods: Participants were 164 Japanese adults with mental disorders who: (a) had never attempted suicide, (b) had attempted suicide before three months, or (c) had attempted suicide within the past three months. We assessed their character traits, life stressors, and coping strategies with a self-report measure. Results: One-way analysis of variance revealed significant differences between the participants’ characters, coping, and stress. Self-orientation and wishful thinking were lower, and self-transcendence, abandonment, and stress were higher among present suicide attempters compared to non-attempters. Multinomial logistic regression analysis showed self-directedness, self-transcendence, and abandonment predicted a high probability of a suicide attempt. Limitations: Causal links could not be established due to the cross-sectional design of this study, and the lack of participant diversity limits the generalizability of our results. Conclusions: Our findings suggest that self-directedness, low self-transcendence, and ease of abandonment predict suicide attempts in Japanese patients with transdiagnostic mental and behavioral disorders.