Wow, welcome to my 50th story on this site! I honestly had another story in mind for the 50th, but it's taking way too long to write.
Anyway, Luffy and Usopp are pretty OOC in this, so I'm sorry about that. It's aaaall for the plot.
"What?"
Luffy Monkey, ten years old, stared at his older brother in shock.
"Dad's . . . dead?" he whispered.
Ace nodded, biting his lip and trying not to cry in front of his little brother.
Luffy, on the other hand, had never had any problem with crying, and began to bawl.
"Come on . . . what kinda joke is this, Klahadore . . . ?"
Usopp Syrup, ten years old, stared at the butler in shock.
He laughed nervously. "You came all the way to our little shack, this late . . . for a prank . . . ?"
Klahadore looked down. "Usopp . . ."
"Come on, Klahadore . . ."
Usopp began to cry.
The next morning, Luffy stumbled down the hall, his eyes red from crying the previous night. Ace, sitting at the table, saw him coming and quickly wiped away his own tears.
Luffy jumped on his older brother and hugged him tightly. Ace embraced him back and they remained like this for a moment.
"How . . . did it happen?" Luffy asked, sitting childishly on Ace's lap as he pulled away. He sniffled again. "It wasn't . . . Yasopp . . . ?"
"Dunno," Ace mumbled. "The hospital didn't say. But . . ."
He laid out that morning's newspaper on the table and flipped through the pages until he found the article of interest.
"See, it doesn't say how it happened," he said, skimming the article and gulping back tears. "It j-just says . . . that they both died in their f-final fight."
Luffy hugged Ace again. Then he frowned and skimmed the bottom of the article.
"Ace?" he said slowly. "It says here . . ."
Usopp came down the huge stairs slowly. He had spent the night in Kaya's mansion—his best friend and the wealthy heiress to her parents' fortune. He found Kaya herself waiting for him at the bottom of the stairs.
"Usopp?" she said quietly. "I'm sorry . . . about your dad . . ."
Usopp's lip trembled and his face screwed up again. Kaya hugged him and allowed him to cry on her shoulder for a bit.
"I-I'm fine," Usopp mumbled, wiping away his tears and pulling away. "Men d-don't cry."
"Well, maybe it's okay not to be a man once in a while," Kaya said gently.
She brought him to the dining room, where Klahadore was starting on breakfast.
"How did . . . how did it happen?" Usopp asked, sitting next to Kaya at the table. "W-Was it—Dragon?"
Kaya shook her head helplessly. "I don't know . . ." her eyes filled with tears too. "He was so nice . . . I can't believe he's gone . . ."
"There's an article about it in the paper," Klahadore said, looking back at the children.
They looked at each other and seized the paper as one. Flipping through it, Usopp found the article they wanted and they skimmed it.
"So . . . no one knows for sure how it happened," Kaya whispered.
Usopp frowned and pointed at the bottom of the article.
"Hey," he murmured. "It says here . . ."
". . . that Yasopp has a son," Luffy said softly.
"So it does," Ace said. "Poor kid."
He glanced at his little brother, whose face was suddenly filled with anger.
"Luffy, what's up?"
". . . that Dragon . . . has a son?" Usopp said.
"Oh," Kaya said softly.
She looked at Usopp, who suddenly had the burning anger of the wronged written on his face.
"Usopp . . . ?"
"Let's go upstairs," Usopp whispered. He and Kaya went upstairs, Kaya glancing back at Klahadore, who chose to ignore them.
"I'm going to kill him."
Ace stared at Luffy. "What?!"
Luffy clenched his jaw. "I'm gonna kill Yasopp's son."
"Luffy, calm down," Ace said quickly. "There's no need for—"
Luffy looked up at Ace, who flinched at the sudden glare of an adult on his little brother's face. "I wanna kill Yasopp!" he yelled. "But Yasopp's dead, and his son's still alive! I-I'm gonna do what dad did—a-and I'm gonna k-kill Yasopp's son!"
"Luffy," Ace said angrily as his little brother jumped off of his lap, "think about this. Yasopp's son has nothing to do with this, doesn't he?"
"But what if he comes after me first?" Luffy demanded. "What if he decides to kill me?"
"Then—"
"I need to kill him first to get revenge for dad," Luffy said, not looking at Ace. "I dunno how I'm gonna find him, but I'm gonna do it."
"I want to kill him."
Kaya stared at Usopp in horror. "What?"
Usopp paced the room with his hands behind his back. "I'm gonna kill Dragon's son."
"B-But—why?" Kaya asked, bewildered.
Usopp clenched his jaw and folded his arms. "Because I can't kill Dragon now that he's dead," he said coldly. "So I have to kill his son instead for revenge for m-my dad."
"Usopp, please," Kaya cried. "I hate fighting! Please don't kill him!"
"There won't even need to be a fight," Usopp said resolutely. "I'll kill him with one shot, no problem."
Kaya's eyes filled with tears. "Usopp . . . what's happening to you . . . ?"
"I just need to find him and get revenge when I'm ready," Usopp said. He looked at Kaya and blinked, dropping to his knees and crawling over to her. "W-Wait, Kaya, please don't cry!"
"I don't want anyone to die," Kaya sobbed. "A-And I don't want you to get hurt!"
"Kaya," Usopp said, his eyes filling with tears as well. "I—I'm sorry—but I gotta do this. I feel like I gotta do this."
Kaya turned away from him angrily. "I don't wanna talk to you."
Usopp stayed by her side anyway. Neither of them said a word.