Soul Power Instruments (S.P.I.) is a Japanese boutique effects builder based in Japan, founded by Kaz Saito. The small operation hand-builds guitar and bass pedals in limited batches and is best known within the domestic Japanese pedal scene, with its work also circulating internationally through shops like TC-GAKKI and secondhand marketplaces such as Reverb.

The lineup covers overdrive, distortion, fuzz, boost, reverb and modulation designs, including the Freestyle (a Dumble-voiced overdrive originally developed as a signature pedal for guitarist Jail O'Hashi), the Viper Nutube Overdrive, the Kaleidoscope, the 78 Distortion, the 78 Overdrive, the After Glow reverb, the Crimson Sky, the SD-1 From Hell and the BlueVague distortion. Alongside its original designs, S.P.I. is also widely associated with boutique modifications of production pedals, notably dual-channel mods with added mid controls for the Boss BB-1X and BC-1X and mid-control mods for the MXR M80 Bass D.I.+.

The brand sits within the broader Japanese boutique pedal scene — a cottage industry of small builders who tend to release gear in short runs and primarily through Japanese retailers rather than through wide international distribution.

Soul Power Instruments has 2 products cataloged on Equipboard, including Fuzz Effects Pedals. Their gear is featured by 1 artist, with the strongest followings in Rock and Pop. Notable users include Haruka Kudo.