One possible reason could be the loss of a dear friend. Naruto values his friends deeply, and if he were to lose one, it would break his heart. For example, if Sasuke were to die or turn against him completely in a way that Naruto couldn't fix, it would be a huge blow.
There's a fanfic titled 'Hinata's Comfort for Naruto'. In it, Naruto is heartbroken after a major loss in the village. Hinata, who has long admired him from afar, steps in. She first helps him by taking care of his daily needs like cleaning his messy apartment and doing his laundry. This simple act of kindness makes Naruto realize that someone truly cares. Then Hinata shares her own experiences of feeling alone and how she overcame it, which gives Naruto the strength to start anew.
Well, the Kyuubi might use its chakra to soothe Naruto's emotional pain. It could send warm waves of its powerful chakra through Naruto's body, making him feel more at ease and less heartbroken.
One good 'naruto heartbroken fanfic' could be 'Broken Promises'. It delves into Naruto's heartbreak when a dear friend betrays him. The story is full of emotional turmoil as Naruto struggles to come to terms with the situation. Another is 'Fading Hope' where Naruto's dreams are shattered, and his pain is palpable throughout the narrative.
A possible plot could be Nightwing getting betrayed by a close friend or ally. Maybe they were framed for something they didn't do, and this led to their heartbreak. For example, if a fellow hero believed false rumors about Nightwing and turned against him, it would shatter his trust and break his heart.
To write a 'naruto heartbroken fanfic', you need to be familiar with the Naruto universe. Consider events that could lead to his heartbreak, such as a failed relationship or the destruction of something he values. Develop the plot gradually. Use descriptive language to show his pain. For instance, describe how his eyes look when he's heartbroken. You can also add flashbacks to enhance the emotional depth.
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.