@Zweit Any suggestions? I can make some pretty wild suggestions. Alright, I'll give you a few.
#1) I see a distinct lack of Japanese folk creatures, and there are quite a few that linger near the water. I'm thinking you should draw a kappa. Not one of those skinny ones, and he shouldn't look like a balding member of the teenage mutant ninja turtles, though that wouldn't be horrible. We need a Kappa that doesn't miss the grind. I'm talking about a swole boy. Giga chad lookin' Kappa. But he's not the sort to start fights or any of that nonsense. He's actually quite refined, and spends most of his days fishing off his boat under the shade of a straw hat.
#2) I see no big scary underwater monsters. It's fun to have really hot murder mermaids but horrifying sea monsters that are impossibly large with rows of teeth, spikes, etc. There are too many real deep sea fish that scare me to recommend one to base a monster off of. Angler fish or those transparent squid would make for a fine baseline I would think. Unless yo wanted to go shark route. Sharks are awesome too. They don't have that exotic flair of true deep sea animals but sharks are always cool.
#3) You have monster girls, but you can never have too many monster girls. I'm thinking a jellyfish girl ice skater. But she's underwater so she skates on the underside of the ice. Maybe she could be doing a sick trick or something. If you were feeling really tricky, her duet partner could be skating on top of the ice. I'm not sure what her duet partner would be upside-down-jellyfish-ice-skater is the important part of this idea.