666 ～サタン～ [Roku-Roku-Roku Satan / 666 Satan]

In the world of 666 ～サタン～, a young boy named Jio possesses the power of the demon Satan, sealed within his left hand. This shonen manga, serialized by Square Enix from 2001 to 2008 across 19 issues, follows Jio's journey as he seeks to become the world's greatest treasure hunter while grappling with his destructive inner power. Created by Seishi Kishimoto, the series is noted for its post-apocalyptic setting, fast-paced action, and the dynamic relationship between Jio and the demonic entity within him. It stands as a distinctive entry in early-2000s manga, blending adventure with a darker take on the classic "demon within" trope.