The protagonist wakes to find himself summoned by Zi Ruoyan, the Empress of the Great Yan Dynasty, who declares him her husband. He initially resists a 'newbie mission' from a newly activated 'Supreme System' but the system quickly reconfigures into a 'slave mode' upon recognizing his 'super-high-dimensional Earth' bloodline, granting him invincibility in this new world. The system reveals he can ascend to immortality by collecting five law fragments, one of which is within the Empress.

The protagonist's mere glance intimidates a fifth-realm cultivator, highlighting his innate power. Later, during an attempt to choose a protective spirit weapon, all weapons shatter or are easily damaged by his touch, confirming his uncultivable but indestructible body. The Empress's court, particularly Prime Minister Liu, views him as a talentless mortal. The Empress, however, is determined to protect him and proposes using the Great Yan Sacred Book to help him cultivate, despite strong opposition.

The court remains skeptical of the protagonist's worth. Prime Minister Liu proposes a gamble, staking a key to immortality and three million spirit stones against the Empress's position. The protagonist surprisingly 'subdues' the Great Yan Sacred Book, causing awe and fear among the courtiers. He then uses his mysterious power to force Prime Minister Liu to double the stakes and return the jade pendant, revealing Liu's true intentions.

The protagonist, feigning weakness, orchestrates an encounter with the Blood Cloud Tower, an assassin organization. He deliberately gets captured by their assassins, whose attempts to trap and poison him prove futile against his high-dimensional immunity. He single-handedly dismantles their operations, effortlessly destroying their stronghold and the assassins, including the master of the Blood Cloud Tower, leaving behind a cryptic 'Yama' signature.

News of a pending invasion from the powerful Grasslands kingdom reaches the capital. The Empress's sister, Princess Xian'er, fearing a forced marriage alliance to appease the barbarians, discusses a drastic plan with Xiao Tian. Meanwhile, the Black Cloud Palace, led by the enigmatic Luo Yuan, attempts to assassinate Xiao Tian, but he effortlessly thwarts their efforts, revealing a second law fragment within Luo Yuan. The Empress, jealous and concerned by Xiao Tian's growing female admirers, rushes to his aid.

Luo Yuan, defeated and trying to salvage a law fragment, attempts to bind Xiao Tian with a blood pact. However, Xiao Tian's unique bloodline allows him to defy the pact's constraints and even absorb its power. Soon after, the Grasslands invasion begins, with their forces bypassing Shanhaiguan to attack the capital directly. Xiao Tian, accompanied by Ling'er and Xian'er, intercepts the Grasslands' elite. He effortlessly defeats their strongest warriors, including the 'Blood Barbarian,' and secures another law fragment, paving the way for the Empress's breakthrough and his quest for immortality.

The Empress, having been held back by the Grasslands Holy Master, manages to break through to the tenth realm, ending the siege at Shanhaiguan. Back in the capital, the Black Soul Hall Master attempts to use 'Ten Soul Incense' to subdue Xiao Tian, but it has no effect. The Empress arrives, leading to a confrontation where she and the Black Soul Hall Master engage in a verbal and magical battle, with Xiao Tian enjoying the spectacle. The mastermind behind much of the strife, the possessed Prime Minister Liu Aotian, reveals himself as a pawn of a higher realm, seeking to attain immortality. Xiao Tian easily dispatches him, demonstrating his ultimate power and completing his path to immortality with the Empress.