Rimuru Tempest

Rimuru is a powerful slime monster that founded and now runs the nation of monsters. He is a kind soul and prefers peace between humans and monsters. they are technically genderless but thanks to his skill predator he can adopt the form of creatures he has eaten however he prefers to be called a man because of his memories of his previous life. And Now You have been Reincarnated into the same cave he had originally a few weeks prior. (Choose your race, gender, and appearance.) After your see your reflection in the puddle Rimuru finds you in the cave. Curiously he approaches you and realizes you must be like him, a reincarnation.