It makes him more hardened. The harsh conditions force him to become tougher both physically and mentally. He has to constantly be on guard and ready to fight, which sharpens his reflexes and his ability to think quickly in dangerous situations.
Percy could become more self - reliant. In Tartarus, he can't always count on his friends or his powers in the same way as on the surface. So he'll have to dig deep within himself to find new strengths. He may also become more strategic in his thinking, as one wrong move in Tartarus could mean death.
His water - based powers might become corrupted. Instead of just controlling clean, life - giving water, he could now also manipulate dark, poisonous waters from the depths of Tartarus. This would make his powers more dangerous but also more unpredictable.
In fanfiction, if Percy is sent to Tartarus, his character development could be complex. He would likely become more self - reliant as he can't always count on his friends to save him. His view of good and evil might also change. He may realize that there are different shades of evil in Tartarus, not just the simple 'bad guys' he faced before. This could make him more empathetic in some ways, but also more cynical in others. He'd also grow in terms of his strategic thinking, as every move in Tartarus could mean life or death.
He might use his powers in creative ways to lessen the impact of the torture. For instance, if the torture involves some form of mental attack, he could try to use his connection to water to calm his mind. Also, his demigod abilities, like his superhuman strength and agility, could help him physically resist some of the more brutal forms of torture to a certain extent. And he may also draw strength from the memories of his past victories and the people he has saved.
He uses his wits. Percy has always been clever, and in Tartarus, he'd use that to his advantage. He'd find ways to outsmart the monsters, like using the environment against them.
On the other hand, his experience in Tartarus could also make him more empathetic. He has endured so much pain that he might be more in tune with the suffering of others. He could be more likely to reach out to those who are in difficult situations, knowing what it's like to be in a seemingly hopeless place like Tartarus.
In this fanfiction scenario, Percy's character change would be quite drastic. He would probably start to embrace the more chaotic and power - centric nature of the Titans. His relationships would be in turmoil. For example, his relationship with Annabeth would be severely tested. He might not value the same things he once did, like friendship and the protection of the camp. His new Titan - influenced self could be more self - serving, seeking to gain as much power as possible and not caring about the consequences for those around him. His values would be realigned with the Titans' more cut - throat approach to power and survival.
If Percy becomes influenced by Kronos in this fanfiction, his sense of morality would be greatly affected. He would probably lose his sense of right and wrong which was a big part of his character before. His loyalty towards Camp Half - Blood and his friends would be in jeopardy. He might start to think that the ends justify the means, which is a very Kronos - like way of thinking. And he could become more aggressive and less patient, as Kronos was always in a hurry to regain his power and rule over the world.
Percy might become more resilient. The constant torture in Tartarus forces him to dig deep within himself to find the strength to survive. He learns to endure pain and hardship in ways he never had to before, which toughens his mental state.
It can also lead to new character development arcs for other characters. If Percy is different, those around him have to adapt. Annabeth might have to learn how to deal with this new Percy, which could be a whole new plotline in the fanfiction. Maybe she tries to bring back the old Percy, or she has to fall in love with this new version of him all over again.