@wolfeng
That is not what happened....
If you read again you will see that he decided to dedicate himself into learning magic in his first life, becaise it was fun and... well... if you could do magic out of nowhere the most logic action is to learn as much as you can about it.
Then the second life he decided that since he already knew all there was about magic he would learn to fight and decided on the sword as his weapom, that he was a hero and employed to fight monsters is just background.
This is his third life, not the fourth, since the life he was in Japan and the one he became the magic emperor are the same.
Basicaly he is a talented and hard working individual that is able to reach the ultmost potential in what he puts his mind into doing and took him two lifes to realize that humans despise those that are too good at something.