If you type "link download manga Gantz" into a search engine, you will be flooded with results. However, many are dangerous or low quality. Here is what to look for:

Gantz is a copyrighted manga by Hiroya Oku. This post explains legal ways to read/download it and why pirated links are harmful.

For academic or archival purposes, some volumes and spin-offs have been preserved on community-driven platforms:

Once downloaded:

The sphere’s lights turned red.