okay so Danny and Talia are childhood friends. How they meet it's up to the dealers choice. Was Talia on a mission? Was Danny in the League of assassins for a while when he was young? Anything
Talia and Danny trust each other and then know each other secrets of course and they did help each other like Talia occasionally helping Danny on time missions or Danny becoming her medical support/bodyguard after missions. He did to tried to help her but when she firmly refused she knew pushing her would only drive her away so he stayed silent. Couple of years go by she meets Bruce they continue talking until Damien is 3 years old.
By that point Talia put all her focus on trying to keep Damian alive and teach him everything she could so he could survive on his own and Danny went on to have his own missions for Clockwork.
As Damien grew Talia started to realize that Damien living with his father might not result in absolute happiness or complete safety recognizing the fact that he has poor emotional intelligence at times or too dense to notice emotional moment or a certain emotion on someone's face. Of course he doesn't do it intentionally but she also recognizes the fact but he's a lot more stubborn and in arguments could lead to multiple possibilities and not all of them very good (she saw Jason she knew the result of what arguments did she saw Jason's older brother move out due to constant arguments)
Talia might love Bruce but her love for her son is greater so she needed someone she could trust and rely on to protect and raise Damian if something ever happened to her and remembered her old friend.
She knew Danny would absolutely protect Damian if anything happened to Talia or Bruce or even Damian's siblings. So in her will she wrote that if anything were to happen to her Damien should be sent to Danny claiming him as Damian's uncle.
So when Talia by some sort of shock kicks the bucket the assassin's immediately go to Damien and read her will to him. Damien being cornered and alone after getting convinced by the assassins that they are just reading her will gave them a chance. After learning about this supposed uncle he had he decided he would go investigate him and to see if he's truly that trustworthy.
He decided to take Jon with him seeing as the address was supposedly in the sky. When they got there they saw a huge Greek styled palace with waterfalls, ponds with mythical fish, pillars, big balconies etc
When they knock on the door a young man in robes comes out looking groggy and confused assuming he just woke up. After Damien introduces himself and explains the reasoning as to why he's here danny he immediately curses under his breath muttering something like "I'm going to drag Talia back" before letting them in.
Danny starts fussing over Damian telling him about how much he's grown in the last time he saw him was when he was 2 years old and with Jon asking questions it dissolved to Danny showing baby pictures of Damien and telling stories , Damien trying to stab Danny to put an end to his embarrassment and Jon snickering.
The whole thing ended with Jon carrying Damian out the door both of them waving goodbye to Danny was Damien still being embarrassed and grumpy.
they continue visiting Danny and always learning something new like time laws , cooking , mental health , about the supernatural , weaving , astronomy , self care etc.
By that point Danny is the safe adult. Someone who will listen without judgment offer a device when needed , comfort console and teaching you something new while making jokes and always telling them to take care of themselves.
Danny has become a Damien's uncle not only on paper but emotionally as well. He's the one Damien searches for when he's struggling or having family issues that he doesn't know how to solve or express. He's the one he calls in the middle of the day after seeing something stupid his classmates did. He's the one person Damien can trust other than his family to keep him safe
To Jon he's a cool adult that always make sure both him and Damien are safe and teach them cool things and giving them good advice. Always making sure that they're okay and always giving them the something new to learn about.
But there comes a slight issue. Danny was under the assumption that their parents knew where they were going and who he was which brings the issue at hand.
Danny being with batman and superman as they all look at each other confused as Danny tries to tell them about Damian and Jons progress with magic.
Safe to say when Danny finds out that none of them even knew who he was they got the scolding of a lifetime with Danny telling them about the dangers of going into a place that your parents don't know going without permission and talking to a random stranger you learned about through a piece of paper one day going on and on about what they're doing was stupid and that he taught them better than that.
Batman didn't even get the chance to try and interrogate him before Danny apologizes and explains who he is and how he knows Damien and Talia basically giving Clark a full report on Damian and Jon and what they have been doing (but not telling them about the things Jon and Damien made him swore never to tell anyone) apologizing again saying he assumed they already knew
After Danny takes both of them to his house and they talk things through Bruce and Clark seem a lot more content and assured around Danny however the looks they give Damian and Jon only give them a look that promises they'll get a lot more scolding when they get home
Ironically enough now both families visit Danny's house as well often talking about whatever random topic and laughing
Damien and Jon may have been caught and they may have a stricter schedule now with rules that's strictly make their parents know what they're doing and the times but at least Danny and their parents get along