Naruto's optimistic personality is a big factor. His ability to always see the bright side of things can rub off on Sakura. For example, if Sakura is worried about a mission, Naruto will be all like 'Don't worry, Sakura -chan! We've faced tougher things and we always come out on top!'. His positive outlook makes Sakura believe that things will be okay.
Naruto is also very empathetic, despite his sometimes goofy exterior. He can sense when Sakura is truly sad. When he cheers her up, he draws from his own experiences of pain and loneliness. He shares those stories with Sakura, making her feel that she's not alone in her struggles. His empathetic nature helps Sakura open up and start to feel better.
One possible scenario could be that Sakura is feeling down because she failed a difficult medical ninjutsu exam. Naruto, being the good friend he is, takes her out for her favorite ramen and tells her stories of his own numerous failures and how he never gave up. This cheers her up as she realizes that failure is just a stepping stone to success.
Sometimes, in fanfiction, Naruto stands up to Sakura when it comes to her attitude towards Sasuke. Sakura might be blindly following Sasuke's every move, and Naruto, having a more objective view of Sasuke, could confront Sakura. He would tell her that she should value herself more and not just revolve her life around Sasuke. Naruto has his own understanding of friendship and loyalty, and he would use that to make Sakura see things differently.
One way to write a cheering up scenario in a Naruto fanfiction is to have his friends come together. For example, Sasuke could return after a long time and they have a friendly spar. During the spar, they exchange words of mutual respect and understanding, which could cheer Naruto up as it shows the bond between them is still strong.
Kurama is often depicted as mischievous in fanfiction. His powerful and somewhat arrogant personality leads him to play pranks on Naruto. He might think it's beneath him to be so closely tied to a human, so he uses pranks as a way to assert some sort of control or just to amuse himself.
Friendship is a very common theme. Naruto and Sasuke have a deep bond, and in these fanfictions, Naruto uses that bond to lift Sasuke's spirits. For example, he might remind Sasuke of the times they protected each other as kids.
Naruto's power is crucial. His physical strength allows him to stand up to Sasuke in a fight. For example, his Rasengan can be a powerful weapon against Sasuke's attacks. His Nine - Tails chakra also gives him an edge, as it boosts his speed and power. He can use this power to quickly get between Sasuke and Sakura when Sasuke tries to harm her, and then hold Sasuke off while he tries to reason with him or find a way to stop his aggression.
It could lead to a shift in the type of fanfictions being produced. If Naruto getting fed up with Sakura fanfiction becomes a popular concept, more fanfic writers might avoid writing in that vein or might try to rewrite the relationship in a more acceptable way, which in turn changes the overall landscape of Naruto fanfictions in the fandom.
Naruto might be shocked at first. He has always seen Sakura as a friend, so being beaten up by her would be unexpected. He could try to talk to her and figure out what's wrong.
One great 'naruto cheers up sasuke fanfiction' is 'A Bond Rekindled'. In this story, Naruto finds Sasuke in a very dark place after a tough battle. Naruto uses his unwavering friendship and positive memories of their past to slowly bring Sasuke out of his gloom. He cooks Sasuke's favorite food from their childhood days and they sit and talk for hours, just like old times.
It can create a lot of drama and emotional turmoil. The break - up might lead to Sakura becoming more independent and focused on her own growth as a ninja. For Naruto, it could also be a turning point in his personal development, making him re - evaluate his relationships in general.