Well, well, well! We have Saitama and Kai going up against each other, but let's be realistic here. This battle is as good as over before it even started! First of all, Saitama is beyond outerversal and beyond omniversal! Even Kai's omnipotent, omnipresent and omniscient powers pale in comparison to him! So, we see that Saitama has superior power, but he is also faster than Kai. Kai could control lightning, but it doesn't matter. Saitama can always keep up with his opponents. He just says "meh" and moves on even if an enemy has speed! Talking about durability, Saitama can take down an opponent with just one punch! Did you hear that? With just one punch! Kai could regenerate, but if Saitama throws a punch and uses his Death skill, then it is game over for Kai! And, if it's a matter of defense, Saitama has Shock Absorption! He is unaffected by the force and power of every attack in the omniverse! So, nothing will affect him, even something like Kai's black fire or throwing a cosmic ball. And finally, Saitama's Serious Punch is something that could destroy everything. It has a power level of 70! Now, even though Kai has the Void God Armor and the Heaven and Hell Katanas, they wouldn't hold a candle to Saitama's Serious Punch. One hit, and Kai is gone! So, Saitama wins this battle without breaking a sweat!