A really cool Young Justice Supergirl fanfiction could be set in a future timeline where Supergirl has become a mentor to a new generation of heroes in the Young Justice team. It could show how she imparts her wisdom and experiences, and how she still has to face old and new threats alike, making it a story about legacy and continuous heroism.
In many Young Justice fanfictions, Supergirl can be portrayed in various ways. Sometimes she's shown as a powerful and somewhat naive newcomer to the team. She might struggle to fit in with Earth's customs while still being eager to prove herself. For example, she could be depicted as being overly enthusiastic in battles, which might cause some initial friction with the more experienced members of the team.
There's a fanfic called 'Nightwing and Supergirl: United Front' which has great character interactions. It shows how they work together in battle and also their off - battle banter which is really engaging.
Perhaps in the fanfiction, the Joker has created a mind - control device and is using it on some of the Young Justice members. Supergirl and Ace must figure out how to stop him and free their friends. Supergirl could use her strength and flight abilities while Ace uses his wits and any special skills he has.
One idea could be a story where Ace teams up with Supergirl against the Joker's evil schemes in the Young Justice universe. Maybe Ace has some special abilities that complement Supergirl's powers.
Another theme is the exploration of different powers. Since Naruto has ninja abilities, Supergirl has super - powers, and Young Justice has a variety of skills, fanfictions often play with how these powers interact. They might create scenarios where the characters have to learn from each other's powers to overcome challenges, like Supergirl learning Naruto's stealth techniques.
Well, one possible plot could be that Supergirl is somehow transported to the Young Justice universe. Maybe there's a dimensional rift caused by some villain's experiment. She then teams up with the Young Justice team to stop this villain from causing more chaos across different dimensions. They could learn from each other's skills and powers along the way.
Another common plot involves Supergirl facing an internal struggle. Maybe she discovers a new power that she can't control, and it's causing problems within the team. This forces her to not only figure out how to master the power but also deal with the trust issues that arise among her teammates.
One possible plot could be that Naruto, through some interdimensional rift, ends up in the Young Justice universe where he meets Supergirl. They could start off as strangers, but quickly realize they have a lot in common. For example, both have superpowers and a strong sense of justice. Naruto's ninja skills and Supergirl's Kryptonian powers could combine in interesting ways during battles against common enemies. They might also have to overcome cultural differences, as Naruto is from a feudal - like ninja world and Supergirl from a more advanced, alien - influenced society in the Young Justice world.
You can start by looking on fanfiction websites like Archive of Our Own (AO3). It has a large collection of fanfictions, and you can search specifically for Young Justice Supergirl ones using the search bar. Just type in 'Young Justice Supergirl' and you'll get a list of relevant stories.