When you search for "download manga," the search results are split into two worlds: Official and Unauthorized.
Locally stored files eliminate loading times and lag between pages.
Thousands of sites offer free downloads of manga that have not been officially released in English. While tempting, these sites often host "scanlations" (fan-translated scans). The risks here are significant:
Let’s assume you want to legally and safely to your phone or computer.
Because aggregator sites usually do not offer a "Download" button to protect their bandwidth and ad revenue, users often rely on third-party software or extensions to chapters in bulk.
The manga industry is notoriously brutal. Mangaka work 80-hour weeks for minimal pay. Every time you illegally instead of buying it, you are contributing to the decline of the industry.
There is now very little excuse for piracy. If you cannot afford $7 for a volume, use the $2.99 Shonen Jump subscription. If you want to archive a series, buy it on Kobo.
Tools like (desktop software) paired with DeDRM plugins can convert your purchased eBook files into universal formats (EPUB/PDF) that you can store on your hard drive forever.