Mystic World: System Wants Me to Cultivate Protagonists!

After finishing dinner at home, Zhao Long was looking forward to a good night's sleep, but unexpectedly he was summoned by a system to a mystic world. Ding! The host can choose any god or demon from the Divine Demon Graveyard to cultivate as the protagonist. From then on, Zhao Long embarked on a difficult journey of cultivating one protagonist after another... The summary is weak, please read the main text!