I Was Enjoying a Quiet Retirement from Tomb Raiding Until the Little Brother Made Me the Fourth Calamity

[Transmigration + Rebirth + The Old Nine Gates + The Grave Robbers' Chronicles + No Female Lead + Fourth Calamity] A wild, imaginative mash-up written as a treat for longtime fans. It has lots of worldbuilding and a slow-paced plot. If you're a new reader and find it hard to follow, I bow and apologize in advance. Please go easy on me. Synopsis: Song Wuji, a time-traveling immortal cultivator known as the Fire Immortal, gets his wish and stays in the little world of The Grave Robbers' Chronicles. On the eve of the Zhang family's civil strife, he races to save Zhang Qiling, whose identity as the Sacred Infant has been exposed. Eager to become Little Brother's adoptive father and master, he soon realizes that something is off about him. Why is Little Brother acting like we've known each other forever? How does he know I have a System? Wait, how does he even know what a System is? Even more absurdly, the Qing dynasty still exists in the real world, and he and Little Brother have somehow entered a game. Song Wuji gazes at the game's gloomy gray sky, at a loss. Little Brother has turned into a gaming addict. What should a “dad” do?