Hi there,
Jav-It does have experimental support for downloading videos from their Japanese storefront. However, that is only avaliable on the Patreon branch of this software. So if you were interested in that functionality, you would need to support me on Patreon to get those features. However, I will say that performance is kind of flakey at the moment, since they seem to reject requests for no real reason. So sometimes you have to try and start downloads multiple times, or just launch the video playback using your browser, then try to start downloads immediately after. I assume this is some anti-download measure, but I'm not sure yet.