I Grind Proficiency to Become an Immortal

In the thirteenth year of Yonghe in the Great Jin Dynasty, chaos reigns as war flames rise, demons and evil spirits run rampant, and bandits plague the land. Li Chang'an, who transmigrates to become the eldest son of a local fortress in Blackwater Valley, awakens a bamboo slip of proficiency. Riding, archery, boxing, swordsmanship, and footwork—all five mortal martial arts—he grinds to perfection in two and a half years. Mortal martial arts reach their peak, yet they are no match for the demons plaguing the world. Since mortal warriors cannot ascend to immortality, he'll rely on the bamboo slip to grind relentlessly! [Boxing proficiency +1] [Breathing technique proficiency +99] Tempering his body, comprehending internal energy, breaking through the shackles of the postnatal realm, and stepping onto the path of Qi cultivation. From a martial artist struggling to survive in a ruined fortress, he grinds his way to becoming an unrivaled true immortal who commands the clouds and mists! — Description from novelcodex.org