So why is it necessary for Luffy to take out a top in an unbelievablly short amount of time to declare war?
I did not say it was necessary.
I'm saying that one possible scenario is that Luffy destroys Kizaru and that this constitutes a declaration of war.
What is preventing Luffy from using gear 5 and pulling a bajrang gun against Kizaru, like Shanks did against Kid with his divine departure, to prevent further casualties and protecting his nakama? Especially considering that Kizaru was the cause of the SHs being split in Sabaody.
Also, this would give him a similar feat than the other yonkos:
- Shanks beats Kid
- BB beats Law
- Luffy beats Kizaru
(- Buggy ?)
However, as I said in most of my messages, this can take any direction. Kizaru can put up a good fight, Kizaru may not face Luffy at all, etc.