According to a Wednesday Sankei News report, a source in the investigation of Kuroko's Basketball threat letters said there is a high possibility that the liquid sent to Sophia University on October 12 was a lethal dose of hydrogen sulfide.

Contact with liquid hydrogen sulfide may cause frostbite. Breathing in the gas can irritate the lungs, while higher exposures may cause a build-up of fluid, severe trouble breathing, nausea, dizziness, confusion, headache and trouble sleeping. Very high levels can cause unconsciousness and even death.

Approximately 10 different places connected with the Kuroko's Basketball manga, anime or the manga's creator Tadatoshi Fujimaki received threat letters with attached powder or liquid substances this month.

Fujimaki's former high school received at least one threat letter. In addition, a publishing production firm in Tokyo's Suginami ward, a Kuroko's Basketball dōjinshi event at Tokyo Big Sight, and the network for the Kuroko's Basketball radio show received threats this month.