This could lead to a lot of drama. The man might start hallucinating from fear, or he could discover hidden passages within the tomb that offer a glimmer of hope.
Well, in such a story, the man could experience extreme panic and psychological trauma. He might also encounter unexpected help or face various obstacles while trying to escape.
If the breathing tube got blocked, the man would likely suffocate. It's that simple. He has no other way to get air while buried alive.
He might encounter hidden treasures or ancient relics.
When a man sleeps for years, there could be many possibilities. Maybe his loved ones have moved on, or the society has advanced in ways he never imagined. Or perhaps he finds himself with special abilities due to the long sleep.
A possible plot could be that Kakashi sacrifices himself to save Rin from a powerful enemy. This would be ironic as usually, Kakashi is the one protecting others. With Kakashi gone, Rin might then discover some secrets that Kakashi was keeping from her. These secrets could change her view of him and also drive the rest of the fanfiction as she tries to come to terms with his death and the new information.
Perhaps the dark elf captcers the man because she mistakes him for an enemy of her kind. But later realizes her mistake and tries to make amends by helping him on his journey. This could involve using her unique skills, like her ability to move unseen in the dark, to protect the man from other threats in the area.
The man might manage to escape through some unexpected means or be rescued by someone who happens to come by.
In such a fanfiction, Obito might seek redemption. He could use his remaining powers to help rebuild the villages he once damaged. Maybe he would start by teaching the new generation about the true cost of war and how to avoid the same mistakes.
Well, Jiraiya being alive could mean a different path for Sasuke. Jiraiya might have been able to convince Sasuke to return to the Leaf Village earlier. He could have used his own experiences and wisdom to show Sasuke that there are other ways to seek revenge and power. And this could have led to a more united and stronger Leaf Village much sooner.
Perhaps the man was testing the taser for its range. He might set up targets at different distances and try to zap them. He could find that the taser's actual range is different from what was advertised. Or he could be testing how the taser affects different types of clothing. He may discover that thick layers of fabric can reduce the taser's effectiveness, which could have important implications for its use in real - life situations like when dealing with a suspect who is wearing a heavy coat.
It's possible that the tomb contains the remains of a powerful shinobi from the past. Naruto could learn about their history and the secrets of their power. For example, if it was an Uzumaki ancestor, he might find out more about his own clan's abilities. This could lead to him unlocking new forms of his chakra or even new ways to use the Nine - Tails' power.