Give users the ability to download manga and save it on their local machine, limited by user roles. It can be extended by a membership plugin to sell VIP package.
Manga Member Download Nulled adds a Download Manga button for each manga. It creates a .zip file for all images and chapters belong to the manga and allow to download and view offline. You can limit the download permission by User Roles. It works will Custom User Roles as you are able to choose any available roles.