It depends. In most cases, 'Heaven' and 'Hell' are capitalized when referring to the specific religious or mythological concepts. But if used in a more general or metaphorical sense, they might not be.
To be honest, it's hard to say. Sometimes stories like this have elements of truth mixed with imagination. You'd have to do some research or ask the creator to know for sure.
The 'heaven and hell naruto fanfic' often plays with the idea of morality and redemption. Naruto, being a character with a strong sense of justice, might face moral dilemmas in these extreme environments. He could encounter situations where his normal beliefs are challenged, like in hell, he has to make deals with demons to save his friends. And in heaven, he might have to prove his worthiness in a different way than he does in the normal Naruto world. This exploration of different values and growth makes these fanfics quite interesting.
A pen could be the key to a portal between Hell and Heaven. A young artist finds an old pen. When she starts to draw with it, she's suddenly transported to a place that seems like a nightmare version of Hell. There are chains everywhere, binding tortured souls. She realizes that the pen has some dark magic. In her struggle to find a way out, she discovers that there's a path to Heaven, but it's guarded by more chains and horrors. She has to use her creativity and courage to break free from this hellish - heavenly horror.
In a world where Hell and Heaven exist side by side, there was a man who had a special pen. This pen had the power to write the fates of people. But the power of the pen was too much for him, and he became corrupted. He started writing cruel fates for people, chaining them to miseries. As a punishment, he was dragged into a horror - filled place that was a mix of the worst parts of Hell. In this place, he saw the chains of his victims and was haunted by the screams from both Hell and Heaven.
It could be a fan - made story that combines the Naruto universe with the concepts of harem (where one character is surrounded by multiple love interests), heaven (maybe a positive or ideal setting), and yandere (a character type that is overly possessive and often violent in love). However, without reading it, it's hard to say precisely.
The characters of the best friends are important. Their personalities will determine how they react to being in 'hell' or 'heaven'. If one is very optimistic, they might see a way out of 'hell' more easily. Also, conflict is a key element. There could be conflict between the friends because of their different situations, or conflict within each friend as they struggle in their respective places. And finally, there's the resolution. How do they come together in the end? Do they both end up in a middle ground or does one pull the other out of their situation?
It might be a fantasy story. Maybe the two best friends are transported to two different realms, one to hell and the other to heaven. In hell, there could be all sorts of terrifying creatures and challenges, and in heaven, it's all beauty and peace. They then have to find a way back to each other and the real world, and their journey shows the strength of their friendship.