Let's start with idea for Naruto fanfiction.
Personally, I like about Obito. His development and ability is like cheating.
And the idea about him to pursue the dream of hokage instead become main villain quite promising.
So, what happen if the one who crushed by rock in Kannabi Bridge is Kakashi and not him.
If that happen, that obviously Kakashi will die. Obito can survive because he is uchiha that be planned to continue Madara's work.
If Obito survive, he will gain mangekyou sharingan. Kakashi's death must be traumatic for him. The team is lead by Minato, it's not strange that Obito adore the speed of Yellow Flash. I think that can be factor why he get Kamui as mangekyou's ability.
Uchiha that awake mangekyou while still have both of eyes will get susano'o.
In this version, though Kamui is cheat that make him like a living ghost. It still have a weakness of mangekyou since he don't have hashirama's cell.
He won't try to use Hashirama's cell in his own. I don't think that MC will gamble his life just base a canon story.
If Obito look some countermeasure, it'll be senjutsu. But it'll be limited by time, it'll be 5 minutes meditation for 2 minutes useable.
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Let's make a plot.
Now Kakashi is death. Obito and Rin is back to konoha. This be great impact for them. They're rarely interact. And Obito feels guilt to the one who rin's love, kakashi.
Later Obito will ask Minato to guide him to perfect chidori. The reason why Obito is interest in this jutsu instead rasengan is that can become living proof of Hatake Kakashi.
Like Kakashi, he will become anbu once Minato become hokage.
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Madara
He always look in uchiha clan, even if he don't get Obito, he will look another successor. In that time, great war shinobi is happen and a lot of child be send to battlefield. And if he can't get uchiha, he already set his eye to Nagato.
But how about the change of history will attract someone who more dangerous than Madara?
Let's says.
In some mission, Obito accidentally have a contact to Jigen.
Otsusuki clan have ability to read destiny like toad sage. When he look into someone that have great destiny that already change will he make a move?
Otsusuki is ancient being that possess vast knowledge. He can get too many subordinates if he want.
Obito's destiny can be threat to him because Kamui have ability to travel between dimension.
So if Jigen come out earlier, the very first that will b recruit is Madara if he is not death yet. Later is Orochimaru.
Having Orochimaru in Jigen's side is more dangerous than Amado loyal to Jigen.
Orochimaru want get immortality. Otsusuki's karma seal is more profound than his reincarnation technique, there's no greater temptation beyond it for him. Even more, exploit white zetsu or creating homunclus vassal have higher chance to success under him.
Based of operation will be amegakure. In the canon, this place is like heaven for criminal, even more this place used to be battlefield of shinobi war.
Jigen or Otsusuki Isshiki will act as mastermind and won't step up, the reason is clear that to save his power and not break his vassel. And if Orochimaru under his, there's possible that he get a new vassel. But it act as temporary vasal.
That's if Jigen as main villain.
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How about Madara or Zetsu as mastermind?
Instead Uchiha, I think that stuck with initial plan to make Nagato as leader act for moon protect. And since Madara is not get any uchiha as the successor, he immedialtely take Nagato under his wing.
If Nagato don't make some connection with someone like Yahiko, Konan, or Jiraiya, I think that make him be someone like Code toward Jigen.
But in my mind, there's another candidate that possible to success Madara's plan. It'll original character, it's background is Kaguya clan. Another lineage of Otsutsuki like Hyuga, Uchiha, Uzumaki, Senju.
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Obito's life
MC won't be excited like some isekai character. I think that make him to felt some of guilt and think that he have a burden will be better. It suitable with the background of Uchiha.
He will go to Anbu once Minato become Hokage.
And for relation with Rin, at first they keep some distance, they will make up after Rin's kidnapping incident.
For this scene, there's two possibility
- Rescue her before she become Jinchuriki
- Take her with Sanbi back to Konoha.
If the second case is be chosen, there's erupt or prolong shinobi war.
After the incident, They'll start dating. Rin's activity will be limited like Kushina.
In the village, Rin will be work in Hospital and later he will become Tsunade's discipline. Under Tsunade's guide, she will craft her own way, her fighting style won't be like Sakura, but she prefer like Kabuto and Haku. Those two have compability with Isobu.
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Kyubi's attack
It'll go like canon. But there's some different since there's someone else that infiltrate to Konoha. It can be Nagato or someone else. In this arc, Kushina will be die like canon. The different is that Minato will be alive, he will seal Kurama to naruto with another seal technique. It obviously weaker than Eight Trigram and it lock full power of Kurama (not half like canon)
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Uchiha's massacre
It will be like canon. Though in the filler, there's scene that Minato can stop it, but I don't think so. There's Danzo, the one that give fuel in the fire, he also someone that want to collect sharingan for himself. To make that can happen, he make some arrangement that make Obito go out of village in the form of mission.
Itachi who lost his friend, be cornered by his clan and village will be force to make same choice as canon. And his answer will be similar too.
When Obito leard about the tragedy, he go to ROOT, but after fighting in a long time in their base, he finally make some deal with Danzo to pretend there's nothing that happen.
Though this is done, there's huge grudge between them but they cannot aim the neck each other freely.
Since Obito is Uchiha, he will take Sasuke with him.
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Later will similar with canon with him that replace Kakashi's role. Of course based how it'll be interpretation based the situation, there's a lot of change.
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Obito's Team (first assemble)
1. Uzumaki Naruto:
- high mastery in sealing art (he won't learn hiraishin, though this jutsu cool, I don't think that'll suit with Naruto's fighting style that rely on stamina and power)
- adamantine chain that work like Kurapika's [Hunter x Hunter]
- kage bunshin
2. Uchiha Sakuke
- first tomoe sharingan (it's get from Uchiha's tragedy)
- Uchiha's shuriken style and fire realeas
- basic lightning release and weapon coating (be taught by Obito)
3. Haruno Sakura
- high chakra control
- genjutsu
- nin madice
--- *YOU CAN MAKE SOME DEVELOPMENT YOUR OWN FROM NOW* ---