These "Ultimate Ninja 6" fan projects typically pick up the story where the official games left off, often featuring the following arcs: ⚔️ The Hidan and Kakuzu Arc
Because this is a mod, it is typically distributed as a patch or a pre-patched for use with emulators or modded consoles. Most players use AetherSX2/NetherSX2 on Android.
If you are looking for "Ultimate Ninja 6" as a PS2 ISO, you are likely finding one of the following: