Summarize the figures introduced within the Underworld and the plot threads already established.

Ruler of the Underworld: The Sovereign of the Netherworld, a King, yet to make an appearance; The Four Masters of the Underworld (Two of Four): The Blood Master: Ming Luo Sheng; Weapon: The Blood-Light Splendor Blade; Abilities: Wields the power of the River of Styx’s Blood Sea, commanding the Immortal Blood Ranks; Plot Thread: Having acquired the power of the Blood Sea through Karmic Cultivation, he remains hidden in the mortal realm, waiting for the opportune moment to expand the Underworld's influence.

The Weapon Master: Wen Wu Di; Weapon: Silver-White Long Spear; Abilities: Supremacy of weaponry; the spear possesses the power of continuous self-resurrection; Plot Thread: Deeply trusted by the Ruler of the Underworld.

The Five Marquises of the Underworld: The East Nether Fire Marquis, Guan Si Yan: A creature of flame, the only one who managed to shatter the Seal of the Ksitigarbha Relic, who then devolved into a monster and was instantly vanquished by the rampaging Ye Xiu; The South Nether Water Marquis, Xian Tian He: A formation expert skilled in aquatic arrays; after Long Kong broke his formation, he willingly succumbed, releasing the seal’s relic within him; The West Nether Mountain Marquis, Ping Yun Ji: A sky-dwelling entity that utilizes bats for both defense and attack; defeated by the avian divine beast, the Vermillion Phoenix; The North Nether Snow Marquis, Mo Leng Shuang: The Icy Empress, adept at manipulating ice; slain by Old Liu’s Demon-Breaking Sword, which consequently released the Ming Luo Sheng Blood Rank from within her body, causing Ming Luo Sheng to manifest and resulting in her own demise; The Fourth Border Marquis, Liao Wu Jun: A mysterious figure hailing from the Celestial Sea Realm, who lurked within the Underworld seeking a passage to invade the mortal realm; possesses the enigmatic Phoenix-White Feather Fan of the Celestial Sea Realm; abilities unknown; coerced into vanishing by Ming Luo Sheng.

The Ji Du Tyrant, Sha Jun Tian Xia: Weapon: The Emperor’s Imperial Executioner; The Tyrant of the Demon Realm; resurrected with absolute power due to the shattering of the Ksitigarbha Seals within the bodies of the Five Marquises of the Underworld, rendering him unmatched; currently resides on a mysterious floating island in the East Sea, biding his time to seek an opportunity to restore the Demon Realm to its former glory; the Emperor’s Imperial Executioner cleaved through Ye Xiu’s Scythe of Death…