Tensei Shitara Dainana Ouji Datta - Node Kimama !link!

You're referring to the anime and light novel series "Tensei shitara Dainana Ōji datta node, kimama ni shite Nigenai" or "The 7th Prince of a Powerless Nation"!

Instead of hiding his powers to live a quiet life, Lloyd uses his royal freedom to conduct absurd, borderline dangerous magical experiments completely out of the public eye. Unforgettable Characters

The story begins with a mediocre mage in modern Japan who dies in an accident. In his final moments, he laments that he didn't have enough time or talent to master magic. A god, hearing his wish, grants him a reincarnation with a cheat ability: he retains all his memories and is granted "Trinity" magic—a power that defies the laws of the world.