|Use||Injures Quincy who have stolen a Bankai by introducing Hollow Reiatsu to their soul.|
|Created By||Kisuke Urahara|
|Used By||Tōshirō Hitsugaya|
Shin'eiyaku (侵影薬, Shadow-Raiding Drugs; Viz "Shadow Infiltration Pills") are pills designed by Kisuke Urahara to help Shinigami who have lost their Bankai to Quincy Medallions. By temporarily causing the user to Hollowfy, it effectively makes the Bankai "poison" for a Quincy due to their inability to take in Hollow Reiatsu without their souls being destroyed in the process. The pills are taken through any means of physical contact. The effects were first seen when Tōshirō Hitsugaya's stolen Bankai, Daiguren Hyōrinmaru, broke and suddenly injured Cang Du. The Bankai then gradually returns to the Shinigami owner, with an addition of the Shinigami being Hollowfied, such as Hitsugaya gaining a mask over his left eye.