Kakashi father to Jason Todd
Kakashi is killed sacrificing his life for Naruto, but he wakes up in a infinite white space where a voice tells him he can either go beyond or he can help a young man who needs it.
Kakashi excepts and is sent to the DC universe getting all relevant information (gotham,heros ,vigilantes (not their identities), meta humans, technology and money.)
For the first couple of weeks Kakashi keeps seeing people in trouble and his training kicks in so he ends up saving them and injuring the criminals badly.
Before he helped anyone he would put on his old anub mask.
Soon the rumours around Gotham where talking about a new Vigilante.
He meets red hood they fight a couple of times but Kakashi never injured him but soon they team up and after the first team up they start to team up more while becoming friends.
The bat clan especially batman are not happy with Kakashi's vigilante alter ego and they try to stop him but Barbra, Tim and Bruce couldn't find anything about him even when they discovered his identity they couldn't find anything.
Nightwing fights him but kakashi easily beats him without even using his chakra, so batman tries to stop him where Nightwing failed but he fails to as Kakashi didn't let him even touch him as he doged while taunting him.
Kakashi and Jason bond extremely well and kakashi shows him the abandoned house that he fixed up, and soon after Jason keeps staying there longer and longer Kakashi invites him to live there.
Kakashi soon then becomes a father figure to Jason and after a takedown goes wrong and Jason is hit with a drug that lowered his inhibitions he confessed about what the joker did to him and how batman his adopted father refused to kill the man that killed his son and has killed thousands of innocent people.
So kakashi filled with rage breaks into arkham and kills the joker in the most agonizing way possible and writes enough is enough on the walls.
Before returning home to Jason Staying guarding him all through the night and when Jason wakes and has recovered Kakashi Tells him that the joker is dead, he had killed him and he is sorry if he wanted to kill him himself but he couldn't allow the joker to live after what he had done to his son.
When he and Jason both realise what kakashi had just said their eyes widen. But kakashi soon recovers telling Jason he might see Jason as a son but Jason doesn't have to seem him as a dad.
(Or something like that where a character from Naruto (or any other show) is transported into the DC universe and becomes a father to Jason Todd.)