SPR3 is an image archive format used in Persona Q and Persona Q2. It contains one or more CTPK files along with image mapping information. As such, it is often used for storing interface elements such as experience bars or status effect symbols.
Kukkii is a part of the Kuriimu suite of editing tools. It is capable of displaying the first image in an SPR3 archive, as well as importing and exporting it as a PNG. It can be found here.