Sayonara, Zetsubou Sensei Vol. 13 (manga)

Teachers are supposed to inspire the younger generation to follow their dreams and achieve great things. Our hero, Nozomu, is not that teacher. Nozomu's probably the most depressive man in Japan - so depressive, in fact, that every little setback in life inspires yet another suicide attempt! But then why is being in Nozomu's class such a blast? Is it his quirky and endearing students? The bizarre adventures he leads them on? Or is there something after all to the "Power of Negative Thinking"?