The tragic stabbings in Tokyo involving a former boyfriend underscore rising mental health issues among young people. Authorities are examining the incident to address underlying distress among the youth.

The day that Taiki Hirokawa stabbed his former girlfriend to death in a Pokemon store in Tokyo had started like any other, his mother told police. She and her son had breakfast together and nothing appeared out of the ordinary. Hours later, security camera footage caught 26-year-old Hirokawa walking straight into the store, pulling out a knife, going behind the counter where Moe Harukawa, 21, was serving customers, and repeatedly slashing her in the neck and chest before turning the knife on...