Solved by using guide posted by user Yurionice.
Translating Kirikiri Games: A Step-by-step Guide
Tools needed: A game, KrkrExtract, Notepad++
Install KrkrExtract.exe and KrkrExtract.dll to the game directory. Other files in the folder should include data.xp3 and the game's executable file (game_name.exe), as well as savedata and plugin folders.
Drag the game's executable file to KrkrExtract.exe to launch it. It should launch both the game and KrkrExtract.
Drag the data.xp3 file to KrkrExtract window. You do not need to mess with any of the settings or press any of the buttons. It should automatically create a new folder in the game directory called KrkrExtract_Output. Within this folder should be a folder called data.
Remove the data.xp3 file from the game directory. You can move it to another folder elsewhere on your PC, or just delete it.
Remove the data folder from the KrkrExtract_Output folder and place it directly into the game directory. The KrkrExtract_Output folder should be empty now, so you can delete it.