The not-Fishman Fishman vs the Magma Admiral!
This fight drives me insane because in almost every scenario it's over in a flash. Nonetheless, this one interested me so much that I decided to go for it anyway.
I don't regret this at all.
Location: It doesn't really matter.
"Water Style: Exploding Water Shockwave!"
Akainu tries burning the water as it surrounds him, but he can't get enough Magma out. He's pumping out Magma desperately, trying to evaporate all the water. He can hear fanboys crying in the distance, so he activates Haki to appease them for a few moments, but it doesn't do anything. He's just a drowning man standing there while he continues to meet the incoming ocean with a swimming pool of magma. He knows it's useless, though.
A fanboy approaches him, tears in his eyes and says "You're a Marine Admiral. You shouldn't be underestimated". How the hell does that help? At this point the magma around him as cooled to black stone, but he climbs atop it and continues a more voluminous form of Meteor Volcano. There's no time to think. The water's already over his head. He tries protecting himself in a ball of magma, but eventually it cools and hardens around him.
"Water Style! Water Shark Bomb Jutsu!"
Kisame pops the ball with some Water Shark Bombs. The water floods in. Akainu drowns. Fanboys cry.
The tear-stricken faces of the fanboys create a sombre mood, and they sit there wailing at the sight of Akainu's soaked, defeated body; all the time asking "How? He was an Admiral 2 stronk 2 looz. Even beated Aokiji after 10 days srtaihgt".
Suddenly, one of the fanboys' faces lights up, and a smile slowly breaks over his eyes and mouth. With a renewed vigor, he valiantly approaches Kisame, spits at the floor next the shark-man's feet, smirks arrogantly at him and says:
"Zoro would've smashed you."