
With Kizaru being able to blitz Snakeman Luffy, its clear that Luffy needs some sort of an answer to Kizaru's light speed. What he used against Katakuri and Kaido won't be enough.
While G5 is fast, it doesn't inherently give Luffy speeds that can match Kizaru's. That being said, due to how versatile G5 is, Luffy could theoretically use it in an imaginative way in order to gain immense speed. What could this be?

I think lightning could be the answer Luffy is looking for. While lightning isn't as fast as light, it is still extremely fast. About 1/3rd of light speed. Combine this with Luffy's FS, and he has a possibility of tagging Kizaru if he can leverage these two abilities.
My guess is that in order to do this, Luffy won't be able to just grab and throw lightning like he did with Kaido. Rather, I think Luffy will create some sort of a weapon made from lightning. G5's rubberification would allow Luffy to reshape lightning into any form he imagines and then solidify it with haki.
Ultimately, by creating a lightning weapon and maximizing his use of CoO, Luffy will be able to tag Kizaru in spite of his light speeds, allowing him to win this fight.