I've seen neither series, so cannot comment on anything related to that...
My not knowing the main series referenced made me hesitate to reply, but figured I'd throw some possible ones out there.
Based on comments in the thread, X-Men would be best bet as was already stated. However, some other possible hits come to mind. For example:
In this, Ranma learns to do firebending, like Avater, I consider it a 'esper' type ability as described in this thread, though the story hardley focuses on :it
R-MULTI 'Grand Tour' by DrunkenGrognard - [Dld Date=07/15/2009] - [Dld Size=653kb] - [Dld Files=21] - [Status=Complete]
In this, Ranma and Nabiki learn of innate powers they have, and have a destiny to unfold for them. Ranma's is fire.
R-TB 'Darkness Ahead' by Dark Phoneix - [Dld Date=06/15/2001] - [Dld Size=140kb] - [Dld Files=7] - [Status=Inactive]
The following might apply, he becomes a mage type person, but also seems telekinetic.
RANMA 'Astrild's Restaurant' by Skysaber - [Dld Date=11/26/2004] - [Dld Size=131kb] - [Dld Files=4] - [Status=Inactive]
Following might apply, most of the Nerima cast gets some sort of special ability.
RANMA 'God Seed' by HitmanPAC - [Dld Date=01/18/2009] - [Dld Size=566kb] - [Dld Files=13] - [Status=Inactive]
Following might apply... the ability to understand the universe... A technique Ranma learned from of all things a scroll made by Nabiki Tendo...
RANMA 'The Ultimate Technique' by mikebreslau - [Dld Date=06/26/2009] - [Dld Size=118kb] - [Dld Files=8] - [Status=Complete]
A similar story to the above, sadly though unfinished. May or may not apply.
R-OMG 'When Bakas Learn' by Bluefurball - [Dld Date=10/02/2003] - [Dld Size=229kb] - [Dld Files=4] - [Status=Inactive]
I do not know if it really counts, but most Ranma/Dungeon Keeper crossovers have him gaining abilities as a Keeper that might apply.