This is a collection of ideas i had that i wish would be put into actuality so, anyone can use these ideas though, if you do i ask that you message me because i would love to read the story's that came from them. cool
A fan fiction where oroochimaru finds a child (Naruto or OC) with healing factor that allows the kekkai genkai transfers to work and orochimaru passes that healing factor to the other applicants (all done publicly since there is no need to hide it) so, orochimaru becomes good/stays in village there will be a bunch of kekkai genkai users but, only a few( possibly just the clan children because they have enough chackra at that age) because those were the ones compatible with the healing factor
try using Harry Potter as a baby that appeared and his "healing factor" is a mutation caused by magic or just is magic. Oroochimaru discovers this when they do blood tests upon his entrance to the village. Harry is adopted by oroochimaru and is the only one that can hold multiple kekkai genkai.
When trying to work the senju bloodline he discovers that instead of it being a single power (mokuton for instance) it is a special gene that changes per person to give someone a extreme proficiency in a certain field. (What could happen is that oroochimaru over strengthens this causing the MC to be easily able to adapt to a ninja field :so it's like he/she will struggle a bit in the beginning of learning of a field but, the longer they work on it the better they get at it: heck anyone with senju bloodline basically has a personalized kekkai genkai)
Instead of straight out giving them a kekkai genkai how about giving them(clan kids) a second affinity (of their choice or otherwise) with which they are able to recreate an elemental release.
Or with Naruto part of the aburame clan and he was placed there because the bugs can eat some of the kyubi chakra that was overloading the seal causing the bugs to mutate and change (possibly extreme adaptability as in they change on a moments notice to fulfill an extreme circumstance) also allowing Narutos intelligence to show.
Infinite chakra regeneration (based off of infinite mana regeneration) so an oc that knows a little about Naruto has a system interface that just shows stats and his trait which is infinite regeneration of chakra where he has a tiny pool of chakra that will increase later on but, because of it he can only use jutsu that has a small cost (but is able to use shadow clone because clones also get infinite chakra) so he can only spam low ranks causing him to invent jutsu and master beginning ones.
A gaming system where you can include other various universes (anime, games, etc.) as mods takes place in Naruto by OC academy student
my hero academia one can allow him to give people quirks as if they were in that universe
Naruto finds a gamer book but, instead of giving him a gamer system it gave one to kurama (9 tailed fox)
The upgrade system in the real world which would turn it into a cultivation world sort of like how it happened in the kenji the Shinobi craftsman.
A reincarnation fic OC where a person who was put through a character creation andfor clans he hits random and ends up with a bloodline that enhances shadow clones (can take more hits, gives him more chackra, etc) uses them for missions, studying, training(even the physical type), bunch of stuff
Where someone reincarnated into a sekirei that was not shown yet (may or may not have gamer system)
A fairy tail fic where an OC try's to master all support magic in attempt to bring them back from being lost magic like basic healing magic.
A fic where the yondaime is able to split the chackra of the kyubi into many people
An oc becomes a sword Smith in Naruto and helps out by selling weaponry. In his experiments with chakra and sealing he figures out how to enchant blades during the forging process adding ability's to them through intent.
-Fanfic where an OC will wake up as an orphan in the Naruto( or runes for Potter verse) universe decides safest way to survive is to open a shop then sell things that have seals on them creating legendary weaponry
A fanfic where Naruto becomes great friends with shikamaru which ends up motivating the Nara into training with Naruto which rectifies the issues he would have experienced in the academy and shikamaru puts that genius to work for training.
If one of the dojutsu clans(or a break off of one of the clans) from Konoha had a policy to share their kekkai genkai ( either a clan saving eyes of dead members who allowed it then giving it to people the clan really trusts / or a tradition where if a member of the clan has a person they become really close to such as friends, teammates, or possibly spouses that they would switch one of their eyes with them.) that they trust.
A fan fic where someone(Naruto) got a very limited ability from the gamer skill set such as just ID create and escape or a status menu
The kyubi chakra is mentioned to have abilities to mutate creatures what if Naruto stumbles upon this ability ,due to kurama dieing leaving the chakra inside of Naruto which basically makes it a massive secondary source of chackra that regenerates at an insane rate but can't be used for standard jutsu due to the caustic properties of the kyubi chakra, and ends up experimenting with it mutating different creatures till he has enough control to mutate his team giving them animal qualities or superhuman abilities.
Fanfic where oc joins marvel movie universe by becoming magneto just before start of the movie(increases in ability due to figuring out more uses) or as night crawler where he seeks out the X-men before days of future past movie (or put them in avengers marvel cinematic universe like the one fanfic about the infinity gauntlet)
Fanfic where shiro from fate/stay night gets put into the one punch man universe and faces some of the villains there.