Create a folder where you're going to dump all of the files.
Press F12 in your browser, go to the network tab and start a scene in game.
A "voice_still_{id}" should stand out, right click and open it in a new tab to save it to your folder.
Above the voice_still request should be two more requests that are just the {id}.
One of them is JSON, just right click "Save Response as" and save it as {id}.json
The other is the spine file right click and open it in a new tab to save it just as {id}.
You should have 3 files
voice_still_{id}
{id}.json
{id}
Repeat this for every scene you want to add to your viewer. Put every file in the same folder.
With Python and UnityPy installed
Drag and drop the folder on to the python script and let it work.
The script will create a folder that can just be dragged and dropped into your viewer folder.
Run the patcher and patch Otogi scenes.
To create thumbnails open your viewer, press F12 and go to the console tab
Type otogi.thumb = true
Open a scene and you can take a screenshot with something like ShareX
Rename the image to OTOGI_{id} and convert it to jpg if it isn't then put it in your thumbnails folder.
If you have older files from Otogi Frontier (before baked in censorship?) then you may need to run the script from the commandline
otogi_convert.py rip_folder original
Will add a line to the spine files to let the viewer know they need to be positioned differently.