Characterization is key. A great Birdflash fanfiction really nails the personalities of Robin and Kid Flash. It shows their friendship, banter, and the unique dynamic between them. Also, an interesting plot that either fits within the Young Justice universe or creates a new and exciting scenario for them is important.
You can start by looking on fanfiction platforms like Archive of Our Own (AO3). It has a large collection of Young Justice fanfictions, and you can easily search for Birdflash ones using the tags. Another option is FanFiction.net, though the tagging system might not be as precise.
The exploration of their different backgrounds is also a common theme. Robin comes from Batman's side, while Kid Flash has his own backstory with the Flash family. Fanfictions often use these differences to create interesting dynamics between them. They might struggle to understand each other's perspectives at first but then learn to appreciate and use them to their advantage in their relationship and in their superhero work.
Some members of Young Justice could be embarrassed. For instance, if there are romantic fanfictions about them that are a bit too cheesy or if their weaknesses are overly emphasized in a not - so - flattering way. But others might be really intrigued and want to explore more of what the fans think about them.
I'm sorry, but I can't directly recommend lemon (sexual - themed) fanfiction as it often violates the terms of use and ethical guidelines. However, you can try searching on fanfiction - dedicated platforms like Archive of Our Own (AO3) and use the tags 'Young Justice' and 'Birdflash' to find appropriate non - lemon stories about the pairing.
Some of them might be amused. They could find the different takes on their characters and stories quite entertaining. For example, Superman might chuckle at a fanfic that has him in a comical situation.
The more idealistic members of Young Justice like Robin might be immediately suspicious of Loki. He represents chaos and trickery, which goes against Robin's sense of order and justice. He would probably try to keep the team away from Loki until they know his true motives.
The team is devastated. Artemis might go into a deep state of grief and blame herself for not being there to protect him. Robin could become more withdrawn and focused on finding out who or what caused Wally's death. Superboy might struggle with anger, feeling like he should have been stronger to prevent it.