I will never say that Leo's sacrifice didn't save them. I'm never going to say that it didn't give them everything they needed to win the war. But he didn't win it for them, he destroyed the leader and the most powerful of the bunch but left the army.
The explosion did make an unexpected difference though, one no one wants to talk about because they don't even want to think it really happened. Maybe it was knowing that he did it willingly and no one could ever survive that, or maybe it was seeing Piper and Jason falling from the sky from the force of the blast. Maybe it was watching Frank leading an army next to Reyna and realizing...Both of them were sixteen. Sixteen. Maybe it was seeing Nico and Hazel fighting back to back as they took down monsters, roaring in pain over the deaths they could feel. Maybe it was realizing they were both fourteen. They were barely teenagers. Maybe what happened was she went back to back with him and their blood mixed, dripping and gushing from their wounds and mixing with the upturned soil and grass. Maybe it was everything. Maybe it was nothing and he just cracked.
But everyone felt the shift in the air as he stalked forward like a bear, waiting for you to stand up and challenge him. Everything froze as the demigods all moved behind him, Hazel and Nico on his sides. His grin was devilish and his eyes were like a raging sea. Unforgiving, uncontrollable and angry...so angry. "No one else is going to die today..." His voice was a whisper but it moved like echo's in a canyon, "...but you." And then he slammed his sword into the ground, Frank's eyes widening as he shoved people back.
Maybe it was the sheer force of his will or maybe the two of them helped more than they let on. But even before he roared, the ground was cracking and thrashing beneath the monster's feet. The ground turned into waves like that raging sea, taking anything that couldn't get away and suffocating it. It seemed to grab hordes of monsters, even the spoils left behind and broke them apart, grinding them into monster dust. It left the bodies and the wounded alone, even moving them to the edge where demigods could grab them and take them away.
It wasn't going to be enough, not until there were more of them standing next to him. Children of Demeter and Ceres, Hecate and Trivia...Pollux who used vines to drag back anything that tried to flee or get to them. Children of Nile and Tyche who lent their luck and victory. Children of Ares and Mars who lent their strength and chaos.
When it was over, the earth was calm and left no evidence of what had just transpired, no dust or blood...just tilled soil.
When everyone was awake and healed, no one spoke of what had happened. Old campers would return and jokingly ask who mowed the hill and others would just stare at them blankly. Newcomers would arrive and remark that it looked like the face of the hill was burned. Someone asked why Thalia's tree was spared.
Percy's only response was, "They're scared of me because of my dad. Now they'll realize they should be scared because of who I have at my side."