There is only one file type that uses the .UGOIRA extension:
Ugoira Animated Image File
A UGOIRA file is an animated image file created by pixiv, a Japanese online community of artists. It contains multiple illustrated .JPG or .PNG frames that are displayed in succession as an animation.
The Ugoira format is designed for creating animations on the pixiv.net site. UGOIRA files are similar to animated .GIF files and improve on the GIF format as they are not restricted to 256 colors and are commonly smaller in size.
NOTE: UGOIRA files can be opened by Honeyview, an image viewer for Windows.
Updated: January 29, 2016