In my opinion, it's really hard to say who would win. Jason has his Roman powers which are quite formidable, like his ability to control the winds. Percy, on the other hand, has his water - based powers which are extremely powerful especially in the right environment. In a fanfiction, it could really go either way depending on how the author wants to write it. Maybe they could end up not really fighting but joining forces against a common enemy.
If we look at their personalities as well, Percy is often more impulsive which could either be a strength or a weakness in a fight. Jason is more by - the - book. In a Mark of Athena fanfiction, if the fight takes place near water, Percy will definitely have the upper hand. He can use the water as a weapon, a shield, and a means of transportation. Jason would have to rely on his other powers like his strength and his limited control over air currents. But if it's in an open area, Jason's ability to fly and strike from above could give him an advantage.
Chapter 148, ", The Murder Jar", is the clearest early answer because it turns Green Skins's situation into a concrete plot event. The chapter turns that into something concrete by moving from Fighting is a matter where the winning side always ends up with more... to Setting aside those nimble devils, there were more than three....
Chapter 191, ", Special Forces", is the clearest early answer because it turns Special Forces's situation into a concrete plot event. The setup is Flying into the stars to find another home wasn't a reliable option., but the pressure keeps building through In contrast, staying in the Union and living a stable life was a good....
Chapter 318, ", Heijian Star Strategy", is the clearest early answer because it turns Gu Hang's situation into a concrete plot event. The chapter turns that into something concrete by moving from But even at this stage, it was only a matter of repelling one attack... to The main reason he could act now was that the political landscape of....
Chapter 207, ", 7777 points of grace!", is the clearest early answer because it turns Ge Wajia's situation into a concrete plot event. It opens with But after some time, they still managed to do it. and closes on The number of Blessing Points offered as a reward was substantial,.... The key payoff is that the chapter closes with And the greatest gain of all was averting a potential world-ending crisis!, which gives Ge Wajia a stronger narrative position and pushes the power growth onward.
Chapter 319, ", Iron Curtain Queen", is the clearest early answer because it turns Queen's situation into a concrete plot event. The chapter turns that into something concrete by moving from We will prepare for the worst, and we shall fight a desperate battle... to The Kingdom's military thinkers wracked their brains with the limited....
Chapter 202, ", Airdrop Assault", is the clearest early answer because it turns Matins's situation into a concrete plot event. It opens with When a light curtain appeared around the sea platform, blocking all... and closes on The twenty S-grade Specification Weapons on the Escort Ship, even if.... The key payoff is that the chapter closes with Secondly, he was doubtful that if they retreated this time, how would they gather more intelligence later?
Chapter 349, ", Killed, Bring the Head Back", is the clearest early answer because the violence around Demon Hunters becomes final instead of hypothetical. The setup is He had originally planned to haul away several train cars, but now..., but the pressure keeps building through The goods that could be taken had already been arranged and would....
Chapter 285, ", a heavy punch must be thrown.", is the clearest early answer because the buildup finally cashes out in a real clash. The chapter gives readers a real answer by opening on Blackbird Heavy Industries had lost their intercontinental ballistic... and ending on Current preliminary, rough estimates indicated losses totaling....
Chapter 301, ", Can't You Afford to Play?!", is the clearest early answer because it turns Alliance Army's situation into a concrete plot event. The chapter gives readers a real answer by opening on We aim for a quick victory," but the battles on the Alliance's... and ending on He dutifully played his role as the second-in-command of the Alliance....
Chapter 224, ", A Thought of Union Arises", is the clearest early answer because it turns Polar Industries's situation into a concrete plot event. The setup is Although he had already formed a new Heretic Demon Hunter Squad of..., but the pressure keeps building through But this was, after all, merely a backup plan..