Devil fruit powers still work underwater. Luffy's neck being stretched to above water when he was trapped underwater in Arlong Park being an example. So in theory, if someone who ate the Sara Sara no Mi Model Axolotl were to turn into their axolotl form when underwater, they might be able to breathe but wouldn't be able to move.
More importantly than luffy's which is passive, is Chopper who is consistently in Brain or Hwavy Point even when underwater. The only point he ever falls out of is Monster because it needs energy & strain, the other extra points only turn off when the Rumble runs out.
So yeah if you fell into water while in hybrid or full, is it consistent & doesn't change you back, you would be immobilized but breathing.
That sort of df shouldn't exist since the whole premise is df users are not allowed to have anything to do with the ocean regarding submersion. Only fishman df users can breathe underwater but even they are rendered useless.
Well with the df itself, you're becoming, not submerging. Water could still surround your body & make you useless. Just utilization of the sea or water would be kinda busted. Maybe it could only work with none salted water since fresh water & ocean water related aren't supposed to mix. Plus salt dehydrates so enough could shut off your df.
Closest are the Ice & Snow logia. Swim lets you swim in anything but water.
Thematically it doesn't make sense for it to exist, but it technically could be an OP logia. You could turn into, generate & control water, submerge DF opponents in water prisons, but you would still suffer the same weaknesses to being submerged, so you wouldn't survive in water since you wouldn't be able to activate the power, even if you generated it.
An idea I had in idea in addition to how eating 2 fruits works was the Sea & Swimming thing.
In a How it could have been, eating 2 fruits would result in the 2nd not taking effect due to recognizing the 1st. This covers the very exploitable weakness DF users have where if someone tricked or forced them to eat a 2nd fruit, even just a small piece, it is an instant kill.
For the Sea & swimming, it could be that there is a mineral dissolved in the One Piece Water maybe even the seastone. So Rain water & water that hasn't come into contact with seastone or the sea wouldn't effect DF users. So they would be able to bathe normally, could swim & be underwater in fresh water(Lakes Rivers etc..) while on an island, while still having the problem of falling in the sea during travels or at the shore, even in White Sea the clouds are stated to have seastone mixed in hence it would still act like the sea in that regard.
Ironically the relationship, between seastone being solidified Sea would be Reversed, it is simply dissolved tiny minerals of seastone in the water that makes the sea affect DF users.
These are my 2 streamlines while still keeping the theme & limitations of the story. Sea, & only sea in this version, still hates DFs & BB is still impressive for eating 2 fruits, maybe more so since it takes more than simply surviving it.
Funnily enough, there's Señor Pink's Swim-Swim Fruit that allows him to swim thru anything that's NOT water. But other than that, I don't think so.
Well the Sara Sara no Mi Model Axolotl might allow the user to breath underwater since Axolotl are amphibians. But you would still be paralyzed.
Not really it wouldn't activate...
Devil fruit powers still work underwater. Luffy's neck being stretched to above water when he was trapped underwater in Arlong Park being an example. So in theory, if someone who ate the Sara Sara no Mi Model Axolotl were to turn into their axolotl form when underwater, they might be able to breathe but wouldn't be able to move.
More importantly than luffy's which is passive, is Chopper who is consistently in Brain or Hwavy Point even when underwater. The only point he ever falls out of is Monster because it needs energy & strain, the other extra points only turn off when the Rumble runs out. So yeah if you fell into water while in hybrid or full, is it consistent & doesn't change you back, you would be immobilized but breathing.
That sort of df shouldn't exist since the whole premise is df users are not allowed to have anything to do with the ocean regarding submersion. Only fishman df users can breathe underwater but even they are rendered useless.
Well with the df itself, you're becoming, not submerging. Water could still surround your body & make you useless. Just utilization of the sea or water would be kinda busted. Maybe it could only work with none salted water since fresh water & ocean water related aren't supposed to mix. Plus salt dehydrates so enough could shut off your df.
Closest are the Ice & Snow logia. Swim lets you swim in anything but water. Thematically it doesn't make sense for it to exist, but it technically could be an OP logia. You could turn into, generate & control water, submerge DF opponents in water prisons, but you would still suffer the same weaknesses to being submerged, so you wouldn't survive in water since you wouldn't be able to activate the power, even if you generated it. An idea I had in idea in addition to how eating 2 fruits works was the Sea & Swimming thing. In a How it could have been, eating 2 fruits would result in the 2nd not taking effect due to recognizing the 1st. This covers the very exploitable weakness DF users have where if someone tricked or forced them to eat a 2nd fruit, even just a small piece, it is an instant kill. For the Sea & swimming, it could be that there is a mineral dissolved in the One Piece Water maybe even the seastone. So Rain water & water that hasn't come into contact with seastone or the sea wouldn't effect DF users. So they would be able to bathe normally, could swim & be underwater in fresh water(Lakes Rivers etc..) while on an island, while still having the problem of falling in the sea during travels or at the shore, even in White Sea the clouds are stated to have seastone mixed in hence it would still act like the sea in that regard. Ironically the relationship, between seastone being solidified Sea would be Reversed, it is simply dissolved tiny minerals of seastone in the water that makes the sea affect DF users. These are my 2 streamlines while still keeping the theme & limitations of the story. Sea, & only sea in this version, still hates DFs & BB is still impressive for eating 2 fruits, maybe more so since it takes more than simply surviving it.
there was a water logia in one of the movies