(¬‿¬)
You must be registered for see images
Onoki's Defense

Alright, we know this fight takes place in a forest, this means Onoki's flight will give him an advantage against Kisame, who hasn't been known to be able to deal with airborne opponents too well, especially because these shinobi are rare, and
these two have zero intel on each other.
It has been shown that it's very IC for Onoki to start every battle airborne, since his back isn't in such a good state which means flight is a very good way for him to move. He can easily move out of Kisame's range, and since it's a forest, Kisame will have a hard time keeping up with him on foot.
Assuming Kisame compensates for his disadvantage with an Exploding Water Shockwave, which would flood the battlefield, effectively turning it to Kisame's favor. However, this would let Onoki know he's dealing with a Water Style user, and just at what scale his techniques are.
Onoki has two techniques that can influence his weight, making him heavier and thus stronger, sacrificing his speed, or make him lighter for the opposite effect,
You must be registered for see links
is a very good example of that.
Conclusion: Onoki can easily dodge any of Kisame's Water Style techniques by making himself extremely light, who knows what great speeds he could accomplish...
Onoki's Offense
And now for the offense u_u First of all, this match will most likely be settled with a well placed Jinton, which I will explain now.
Jinton has been shown to be a very versatile technique, it can be many sizes, ranging from smaller than a room to
You must be registered for see links
. With this feat, we can say Onoki can easily destroy the entire landscape, effectively killing Kisame. However, you will probably argue that Kisame could absorb it, I beg to differ. Take a look at these scans[
You must be registered for see links
][
You must be registered for see links
][
You must be registered for see links
], you can see that Onoki destroyed Madara's Susano'o, which is made out of chakra, meaning
Jinton can destroy not only all matter, but also chakra. And especially when used on a large scale, Kisame certainly won't be able to absorb the impact.
Now, the second approach would be to use Rock Clones* in order to play with Kisame's weight, since Onoki never likes to get close to his opponents without clones, he can use this to make either Kisame or Samehada extremely heavy by punching it, this doesn't work well for Kisame with his water techniques, and if Onoki actually hits Samehada, it would be unusable at that weight. We know Onoki can influence the weight of anything by touching it,
You must be registered for see links
. So Kisame, being the guy who likes to tank and absorb attacks, is very likely to fall for this technique.
*Rock Clone technique was originally Akatsuchi's technique in the initial translation[
You must be registered for see links
], but has later been changed to be Onoki's technique in the volume release, so it's therefore canonically Onoki's technique.