Ability - This Logia type fruit allows its user to transform their into hot water Steam, as well as control any water vapor or steam in their environment.
In-Depth Description - Before it is eaten, this fruit appears as a very light blue cluster of tiny grape-like fruits with a white stem and tiny swirl patterns.
When transformed into steam the user possesses the natural intangibility of Logia types, but also has the power of flight as steam does. Their steam is up to 450F (232C), well beyond boiling. If the user solidifies any part of themselves, they can increase pressure in that part to either fire off a high pressure jet of steam or send that body part flying like a rocket.
Falling into water is less dangerous for this fruit, since it has the ability to instantly turn any water it comes into contact with to steam. Of course even this has a limit and can be overwhelmed.
Because water can't burn, this fruit is also immune to heat, and its user immune to burns so long as they are transformed. It is also highly resistant to, but not immune, to freezing.
A unique aspect of this fruit is that it has an increased affinity for creating and controlling large quantities of its element, which makes it more suitable for large scale attacks.
Combat Info - The biggest combat usage for this fruit is the natural intangibility of Logia types.
Another technique is manipulating pressure. Steam is quite well suited to this, and the users body can act as a pressure vessel quickly building up until it's released as a jet stream of steam that has the power to even cut through metal or sending a fist flying as a high speed rocket. However in order to do this the body must be solidified thus opening the user up to attack, but if they are they might explode.
In situations where the user is facing an enemy who can nullify their intangibility, the same pressure technique can be applied to their feet which gives them explosive acceleration and power without spreading their body too far.
One of the most devastating techniques of this fruit can be used when the user is near a water source. They can quickly flash large quantities of it into steam and use it as a high speed, boiling hot cloud which can overwhelm entire battleships at once.
Non-Combat Info - The uses of steam outside of combat are great. The most obvious one is as a heat source for cold situations. However it can also be used, counterintuitively, to start fires
.
Of course we can't forget about steam engines. Similar to how Smoker uses his fruit, this one can be used to power steam machines and steam engines of all kinds. Cooking is yet another application of steam heat.
Lastly the ability of flight, or more accurately directed hovering, can be used to travel long distances or scout out locations.