In a 'Percy goes to Tartarus alone' fanfiction, it could be that Percy is on a quest for redemption. He feels guilty about something that happened in the mortal world and believes that going to Tartarus and facing its horrors alone is the only way to make amends. Along the way, he endures extreme physical and mental hardships, but his determination to right his wrongs keeps him going.
Perhaps Percy has to go to Tartarus alone because he believes it's the only way to save his friends. In Tartarus, he might encounter old foes who are now even more powerful. He has to rely on his wits and his skills with his sword, Riptide. He could also make unexpected alliances with some of the creatures there in order to survive and achieve his goal.
In this fanfiction, Percy going through Tartarus alone could involve him exploring the darkest parts of the underworld. He could discover secrets about the origin of the monsters there. Maybe he stumbles upon an ancient power that he has to either resist or use to his advantage. Along the way, he might have visions of his loved ones which both give him strength and also make him homesick.
There's a chance that Percy meets the personification of Tartarus itself. It could be a shadowy, all - powerful being that tries to break Percy's spirit. Percy, being the brave hero he is, would have to resist and find a way to either outwit or overpower this entity in order to continue his journey in Tartarus.
Well, one possibility could be Percy facing his inner demons. In Tartarus alone, he might have to deal with the memories of his past failures and the fear that comes with being in such a desolate place. He could encounter strange and terrifying creatures that test his combat skills and his will to survive.
It could be Tartarus itself personified. As Percy is alone in this terrifying place, Tartarus could take on a form and directly oppose him. It would use all the horrors and challenges of the place to try and break Percy.
He might face numerous terrifying monsters. Tartarus is full of dangerous creatures, and without his friends, Percy would have to rely solely on his own skills and the power of his demigod abilities to fight them off.
Well, one possible plot could be Percy facing his inner demons in Tartarus. Since he's alone, he might have to rely solely on his own skills and memories. Maybe he'll encounter some long - forgotten monsters that test his strength and willpower. He could also stumble upon some hidden secrets about the place that no one has ever known before.
Bob the Titan could potentially be an ally. Since he has some knowledge of Tartarus and has shown kindness before, he might come to Percy's aid again. He could help Percy navigate the dangerous areas and avoid some of the more powerful threats in Tartarus.
One possible plot could be Percy and Zoe facing numerous dangerous monsters in Tartarus. They might have to rely on each other's unique abilities. For example, Percy's control over water could help them cross certain deadly rivers while Zoe's hunting skills could be used to fend off the approaching beasts.
One possibility could be Percy's struggle to survive the harsh conditions. He might have to find new ways to use his powers in Tartarus. For example, the strange and dark magic there could either enhance or limit his abilities. He could also form alliances with unexpected creatures. Maybe he teams up with some of the ancient and terrifying monsters that live there, but they have a common enemy, so they work together for a time.
In the 'Percy goes to Hogwarts alone fanfiction', it's possible that Percy will discover new aspects of himself. Since he's alone, he has to rely solely on his own wits and skills. He could stumble upon some hidden secrets of Hogwarts that others haven't found. Also, he may have some unique encounters with the Hogwarts professors who take notice of his solitary situation and offer him special guidance or tasks.