Reborn into the Other Universe as The Great Phoenix’s Fiancé?

Min Seo Jin, a famous actor who died saving one of his fan's child from a car crash. Dying as a hero after having a good. He closed his eyes without any regret. World where dragon and unicorn are real, where people can cast magic with bare-hand and fly with or without wings. Creatures he never know exist. Seo Jin, now with the name Seo Joon, similar to his last life. Seo Joon grown up as a good and normal child until his twin brother accidentally hit him with a wooden log with ancient amulet plastered to it. Seo Joon got his past memories as a human, now he is a boy with adult's mind in a new world. Political and cultivation business, trying to survive. Not to mention several days after he regained his memories, people from the capital came and told his family that Seo Joon is the chosen one from the oracle, soon to be The Great Phoenix's fiance, one of the highest guardians in this new world. How can this boy survive in this world?