Zengzhang Heavenly King in the South is also known as the Sword King. His magic weapon is a sword.

The sword symbolizes wisdom, and the sword of wisdom cuts through troubles.

The Four Heavenly Kings are the guardian deities of the Heavenly Court in the four directions of East, West, South, North, and South, and each of them carries a special magic weapon to permanently guard the gates of the Heavenly Realm with vast and boundless magical power.

Artist: @davidvnun (Explainer - 156)