Step Back! I'm the True Crown Prince

Crown Prince William is betrayed and killed in his previous life, only to be reborn with a mysterious magic ring that can summon things from the modern world. Armed with this strange power and the memory of how he fell, he sets out to face the people who wronged him. The contrast between an old royal court and modern tools gives him an edge, but he must move carefully if he hopes to reclaim the throne that was stolen from him.