A ninja can have an underwater adventure in an aquarium. He can search the castle in the water and try to find out what is in the treasure chest. He can swim with the fishes also.
That is not a very large aquarium, so a shoal of neon tetras would work well
Good choices would be a pea puffer, spotted puffer, or a figure 8 puffer
type tao and then will see a ninja when you see it type in character editor ninja
kind of he is more like a ninja sorcerer type
Anything labeled safe for aquarium use. Beyond that, it depends on what type of fish you are keeping, and whether or not you have plants, for which type of aquarium substrate (gravel or other lining for the bottom) should be used.
The best type of plant to put in an aquarium is going to be dictated by the type of fish, temperature of water being used, the type of food, and the aesthetic preference you desire in the end product of the aquarium.Going to your local aquarium store and looking at options with someone specifically knowledgeable on the topic would probably be a good investment of time and energy.
Aquarium
It has been noted that Aquariums are big no no's to be placed inside the Bedroom, but since this would be a Studio type place and its very compact, it would be best to place a divider to separate the area where the aquarium is to be placed from the sleeping area or placed where the bed is to be situated.
Go on google images and type in aquarium snails.
Type in 'Tao' and you will get a ninja and everything.
Wind type attribute points
It depends on the type of filter... different filters are designed differently. You would need to tell us the model or type of filter.