Homicides involving dismemberment, referred to in Japanese as bara-bara jiken (scattered incidents), fall into a wider category known as ryōki hanzai (bizarre crimes) — written with kanji meaning "hunting the strange." Typically when minors were involved in such cases they tended to be victims, not perpetrators.

That changed with a shocking murder-decapitation that took place in 1997.

On the morning of May 27, 1997, the head of an 11-year-old boy was found outside the gate of a middle school in Kobe's Suma Ward. Stuffed into the victim's mouth was a menacing note, written in red pen. Identifying himself in cryptic characters that read "Sakakibara Seito," the killer had written: "This is the beginning of the game ... You police guys stop me if you can ... I desperately want to see people die, it is a thrill for me to commit murder. A bloody judgment is needed for my years of great bitterness."