There is only one file type that uses the .KRA extension:
Krita Image Document
A KRA file is an image file created by Krita, a cross-platform, open source raster graphics editor. It is the native format used to save files in Krita and may include image layers, adjustment layers, assistants, masks, color spaces, and other Krita-specific elements. KRA files are similar to working files used by other image editors, such as .PSD files used by Adobe Photoshop and .XCF files used by GIMP.
Updated: June 17, 2019