In some fanfictions, Naruto might initially withdraw into himself. He could focus more on his training to distract from the pain. For example, he might go on long solo missions or intense training sessions in the woods, away from the reminders of Sakura.
If Sakura were to give Naruto a token made of sakura leaves as a symbol of their friendship, and then later break off all contact with him and leave the village, Naruto would be heartbroken every time he saw a sakura leaf. The once - positive association would become a painful reminder.
One possible fanfiction could be that Sakura, in a moment of great sacrifice, uses her chakra to turn into sakura leaves that Naruto has always associated with her beauty and kindness. But this transformation is a final goodbye as she is sacrificing herself to save the village. Naruto is heartbroken as he watches the sakura leaves scatter, feeling like he has lost a part of himself.
One common theme could be unrequited love. Naruto has strong feelings for Sakura, but she may be in love with someone else, like Sasuke. This can lead to Naruto feeling heartbroken as he sees her pine for Sasuke and not return his affections.
A major theme is acceptance. Naruto has to accept that Sakura doesn't have the same feelings for him. In some fanfictions, this leads to him exploring his relationship with his family, like finding out more about his parents. There can also be a theme of new beginnings. He starts new projects or makes new alliances in the village, showing that he is moving forward from his heartbreak.
It can make him more introspective. He might start to question his self - worth. Since Sakura's rejection hits him hard, he could look inward to figure out what's wrong with him or why he isn't good enough for her.
In this kind of fanfiction, Naruto being heartbroken by Rias could be due to a variety of reasons. Maybe Rias betrays Naruto in some way, like choosing someone else over him in a crucial situation. Or perhaps there are misunderstandings between them that lead to Naruto's heartbreak. It could also be that Rias has to follow some rules in her world that go against Naruto's expectations, causing their relationship to shatter.
One aspect could be that the fanfiction shows Naruto's heartbreak in a very visual and emotional way. For example, he might see his parents in a dream - like state and then they disappear, leaving him feeling more alone than ever. It's a way to dig deeper into his character's vulnerability, which was somewhat masked in the original series by his determination.
Betrayal is another big theme. When someone Naruto trusts turns against him, it breaks his heart. It often leads to him feeling isolated and having to re - evaluate his relationships. For example, if Sasuke were to betray him in a more extreme way in these fanfics. And it's not just about the act of betrayal but also the emotional aftermath that Naruto has to deal with. He has to face his own feelings of hurt, anger, and confusion. Sometimes, he might even start to doubt his own judgment in trusting people.
One great Naruto heartbroken crossover fanfiction is 'Naruto in the World of Bleach: A Broken Heart's Journey'. In this fic, Naruto is transported to the Bleach universe and his experiences there, along with missing his friends from his own world, lead to a heartbroken state. It has great character development and an interesting plot that really delves into Naruto's emotions.