Emperor's Fall, Galaxy's Rise: The Return of the Sovereign

The celestial realm is governed by fifteen immortal emperors, with Xiao Chengyuan, the Lingxiao Immortal Emperor, as their leader, who for ten thousand years has protected his younger brother Xiao Yaochen. Unwilling to remain subordinate, Xiao Yaochen uses an ancient heavenly oath to trap the other emperors and launches a sudden coup. Xiao Chengyuan, out of brotherly love, retreats and is ultimately slain, falling into the star sea. His loyal followers secretly preserve his imperial blood and soul imprint, awaiting the cycle of reincarnation. When he returns to the mortal world, he sheds his former mercy, uses his immortal emperor's foundation to break through every scheme, exposes his brother's secret alliance with otherworldly demons, avenges his own death, and ascends once more to the celestial summit to restore order to the great dao. — Description from novelcodex.org