I draw this fan art depicting Luffy and Kaido's battle at the end of Arc Wano. After Luffy has mastered Ryuuou (Advanced Armament Haki), he will use it as his main weapon to defeat Kaido. According to my expectation, he will use his strongest moves to directly hit the scar that Kozuki Oden left on Kaido's body. Therefore, in order to Luffy's attack have the highest damage, Luffy will adjust Ryuuou's form from round to sharp by his will power,  to stab the scar directly and knock Kaido out.

In the same way that Bard the Bowman killed the dragon Smaug in

 The Hobbit: The Battle of the Five Armies.