Why didn't Katakuri kill Luffy, but taught him to be domineering?

At first, Katakuri certainly didn't want Luffy to escape. Luffy not only disturbed the wedding banquet, but also assassinated the aunt, making the four emperors lose face. Katakuri grabbed the straw hat group in the sun.

But with the fight between Katakuri and Luffy, his mind has been changing. From the beginning, Luffy hurt his sister. He should teach Luffy to take it out on his sister. He wanted Luffy to taste his medicine and make him desperate. He will do more damage with the same moves. Luffy was in a mess, but he kept trying to hide. Katakuri was tired of suffocating him with rice cakes. So far, Katakuri doesn't value Luffy, and even thinks it's not worth delaying tea time.

The real change of heart began when Luffy ran away and turned around. Luffy's surprise attack found the real reason why Katakuri was almost invincible. He found that his opponent was not invincible. He ran away in fourth gear and met Bree. At this time, Luffy can completely meet his partner, and Katakuri will never escape from the mirror world. But the desire to defeat the strong kept him, just like Wukong defeated Fresha in Dragon Ball, which should be a fighter's pride and dignity. Because of this, Katakuri showed great respect for Luffy, and even came up with the idea of wooing Luffy to join the menstruation delegation.

After the battle, Luffy was passively beaten, but Katakuri also found that Luffy grew rapidly in the battle, from no defense at all to being able to avoid or resist one or two moves occasionally. At this time, Katakuri regarded Luffy as a threat, and such people must be their nemesis when they grow up.

Luffy's fighting ability is too strong. Although Katakuli has various moves, he can always stand up. At this time, Katakuri has deeply admired Luffy, and his mentality towards Luffy has completely changed. He thinks he is a worthy opponent. Later, Franpei's troubles affected the fairness of the duel. Katakuri stabbed himself with a halberd, making their injuries reach the same level.

In the end, the two showed their magical powers. Luffy opened the fourth gear of Snake Man, and Katakuri became a giant rice cake. This is a battle of their beliefs. Luffy's determination to be one piece is different from Katakuri's determination to be the perfect guardian of his brothers and sisters. Katakuri didn't have Luffy's ambition to be one piece, so he lost, but after World War I, they were both appreciate each other. Luffy covered Katakuli's easy-to-laugh crack with his hat and couldn't stand his humiliation. My aunt has no hope of becoming one piece. She has no feelings for her children. Katakuri knows best that when she sees Luffy, a respectable opponent, she can guess that his future is limitless, just like Karp and Roger.