Runge Runge no Mi

Name: Runge Runge no Mi (Lung Lung Fruit)
Type: Paremecia
Abilities: Runge Runge no Mi is a Paramecia class Devil Fruit that turns the user into a lung-human. The user is capable of breathing anywhere, including underground, underwater, in a close space or even the space. Also, being a lung-man the user has high capacity of the gases he can store inside him, thus he can perform powerful breaths (inhale and exhale large amounts of a gas). However, that doesn't give him survivability over whatever he inhales. For example, if the user inhales great amounts of poisonous gas, they will still be poisoned, or they cannot inhale fire and exhale it without getting burned.

I like it, it has a lot of flavor... But I'm iffy about the underwater thing. You said the devil fruit makes him capable, but not how. If the devil fruit makes him capable by normal unexplained reason, then it would naturally be negated by the water, and as such he couldn't breathe water. Furthermore, I'm really iffy about a devil fruit doing that at all. If you make it so that the fruit changes the lungs like it changed luffy to rubber and there is no changing it, I can see it. But I'm still VERY iffy about the water, seeing as how devil fruits don't directly interact with water in any way. A key ability of breathing underwater is pretty much direct interaction. If you can explain in a way that it isn't direct interaction with water, you have my approval.

Well the part about breathing is something passive, just like Ito Ito makes Doflamingo a stringman and Gomu Gomu makes Luffy a rubberman. As it turns the user into a lung, it would allow him to breathe naturally underwater due to being a powerful lung, without that meaning that he'd be able to survive underwater for ages. He'd still be unable to move and do anything else at all. In fact, it's like a disadvantage from the way I see it as the user could be down underwater, too weak to do anything and survive, while also being unable to die.

The original idea was that the user could be capable of infinitely using a gas he has stored inside his body (which is a lung) so that he could simply recycle the gas over and over again inside his body until he exhaled it, but that would be too OPed. Thus, I decided to stick with the submitted version that allowed him to be capable of simply breathing anywhere. Then again, I can see what your concern is, so it's your call.

Alright, so I'm going to interpret it this way: any non-solid that enters the lungs is passively ingested (for lack of better word) into the the breathing process. Sense water has oxygen, it would work as it will not reverse the physical changes to the lungs that made them function that way. So...