I cannot remember any event where a victim of a fruit user or an object affected by a fruit user came in contact with the sea stone, is there any record until now in one piece?
Question - if a human turned toy by the hobi-hobi no mi or a homie created by the soru-soru no mi came in contact with the sea stone, would the effect revert? Or does the stone affect the user but not the power?
Exceptions I can think of - Kuzan's ice does not melt or change back to water on the surface of the sea.
Well, there is at least one good example of someone directly on contact with water who were still affected by someong power : the Princess of Fishmen.
If you remember, Shirahoshi-ojou-sama was bullied by the evil Vander Decken IX whose power was allowing him to never miss his target (strongly summarized). His power was still effective as he threw a insane amount of projectiles on Shirahoshi's submarine dungeon. His power enchants boththe weapons thrown and the target, so since the power is not disabled underwater, at least this power is not affected by seastone or sea presence.
We also know that demon power users in contact of sea or seastone can't use their power and that is also the reason prison's cells are made of seastone.
Conclusion :
We can assume that :
- there is no such thing as a DF user able to use his power when he touches sea water or seastone.
- Powers are not affected if the user is not in contact of sea/seastone
- If a DF user is hit by sea/seastone, his victims (hobi-hobi no mi toy's for instace will be freed (for good or until the DF user is not in contact anymore ?).
I think this is a minor plot hole of One Piece because it is never really explained how differents types of fruits's powers work in this kind of situation. Guess we have to decide from each power.
Hope that helps.
Source : One Piece Manga and Anime — Vol. 19 Chapter 169 (p. 11) and Episode 106, Smoker mentions that all Marine Headquarters' prisons are made of seastone.
