What substance Tachikawa Yuko used on the Shimada Hideo's parasyte in the art club? Yuko takes a vial from the art kit to use as a weapon against Shimada, in case he turns aggressive.


   He does turn aggressive, murdering 17 students.


The anime shows the label (in Japanese) of the vial.

What substance was that?
The Japanese label is 油彩剥離剤, which translates to paint stripper.


  The principal active ingredient in historically common solvent paint strippers is dichloromethane, also called methylene chloride, which has serious health risks including death.





  Symptoms of acute overexposure to dichloromethane via inhalation include: difficulty concentrating, dizziness, fatigue, nausea, headaches, numbness, weakness, and irritation of the upper respiratory tract and eyes.





  DCM is also metabolized by the body to carbon monoxide potentially leading to carbon monoxide poisoning.





  Prolonged skin contact can result in DCM dissolving some of the fatty tissues in skin, resulting in skin irritation or chemical burns.