Strongest Magic System SMS

Griffin, a very feared mafia, must experience something unusual when he is 20 years old. A strange message appeared in front of him as he fled from the pursuit of a group of people with his younger sister.
As if things weren't bad enough, he fell off the top of a building, but woke up in another world filled with mana, wizards, monsters, magical creatures from fairy tales. And most confusingly, there is a system that keeps him getting stronger.
How will Griffin survive in this other world? And what mystery brought him to that world?
Welcome to the Strongest Magic System.