Douluo: Sowing the Seeds with Tang San, Awakening the Blue Silver Emperor

Li Yue transmigrates as a disciple of a Tang Sect Elder, awakening the Karma System: sow a cause today, reap the fruit tomorrow. He encounters Tang San, who is being bullied by inner sect disciples. Without a second thought, he bestows upon him the Xuantian Treasure Record, forging a great karmic bond at the cost of his own life. After taking the Blue Silver Emperor martial spirit, Li Yue reincarnates into the Douluo Continent. Tang San is still unable to repay the karma, and can only continue to repay it in his next life, serving as a 'cow or horse'. (Li Yue is the male protagonist, don't be misled by the name. The system's presence is not strong. Tang San reincarnates as a girl, but they remain good brothers; Tang San is not a love interest.)