Well, I'm actually also still not sure about the lightning usage in this dome, but it's safe to say that it would hurt both the user and opponent, if they were both inside.
Note that a Kisame-like bio can swim much faster in here.
(Suiton: Mugensame)-Water Style: Infinite Shark Frenzy
Rank: S
Type: Offense
Range: Short-Long
Chakra cost: 40
Damage Points: 80
Description: A highly advanced form of Five Shark Frenzy where the user creates one shark that attacks the opponent, dragging them into the water. Then, the user unleashes a storm of sharks to attack the opponent from all angles and directions, ending up in a water explosion.
Create a shark, let it drag the opponent down, create more sharks, let them attack, boom.
Done!