There's Light In Fire, Natsu

Fire V.S Wind

We had taken out all the people of Eisenwald. Natsu, Happy and I chased after their leader. I was running as fast as I could while Happy carried Natsu at full speed. I tripped a few times, but determination burned in my eyes. (Undertale)

"Come on Hisui! We've gotta beat him to the meeting!" Natsu called. I glared at him, gasping for air.

"You aren't the one running though..." I growled as I looked ahead.

"Aye..." Happy huffed. Soon enough, that killer came into view.

"Happy, NOW!!!" I screamed. Happy swooped down and launched Natsu into that douchebag's face. He was thrown to the ground, breaking a few boards of the train tracks. When I saw Happy faint and pass out, I ran ahead and cought him in my arms. "Thank you." I carefully set him on the ground. Before lighting my hands on fire, I stood beside my brother. Sh*t is about to go down.

*3rd person P.o.v*

The two dragon slayers stood side by side, their marks touching eachother. Erigor just chuckled.

"Do you really think you can stand in my way?" His voice was deep and cruel.

"If we didn't, we wouldn't be here." Natsu spat. He then charged with a Fire Dragon Iron Fist. But Hisui stayed behind to observe. Erigor just cought Natsu's fist, extinguishing his flames. Natsu cursed under his breath.

"Wind can never beat fire!!" Erigor shoved Natsu back with a tornado. He would've landed on top of Hisui, if she hadn't sidestepped him. Her face didn't change from her hard glare as she used her fire breath on the wind wizard. "Didn't you just hear me? Wind can never beat fire!!!" He just blew the flames aside.

"Tsk. If we can't use fire, let's just use our fists. Get up Natsu. I can't beat this guy by myself." Were her last words to him before pushing off the ground with some fire. She nailed Erigor right in the stomach. He doubled over, gasping for breath. Hisui smirked at his reaction and went for it. She kneed him in the chin, gouged his eyes, and kicked him to Natsu.

"Fire Dragon ROAR!!!" Natsu tried basting Erigor while he was defenseless. But just before it hit, he dodged, as it just wizzed past his sister.

《Just a itty-bitty time skip because of the plot》

Natsu cried out in pain as he was smacked into the tracks, unresponsive to anything Hisui said.

"Natsu... you Son of a bitch..." fire started swarming around her. Vains appeared on her forehead, her teeth clenching tight, threatening to break her jaw. "How could you... if you killed my brother, I swear to God, I'll break you my mother fu**ING self!!" She let out a scream of anger and sadness, her flames almost reaching to the sky. Happy looked close and saw tears staining her cheeks. "I WILL AVANGE MY BROTHER!! AND IF I CAN'T WIN WHAT'S THE POINT?!? YOU WILL DIE BY MY HANDS!!" She didn't notice that Erigor's wind was being pulled in by her rage of emotional fire. Erigor was actually suprised at this random burst of power.

"Hey Hisui!" Happy called. She spun her head, her hair flying everywhere. "I didn't wanna tell you this now, but Natsu's dead..." Happy forced some tears to his eyes to make it look real. Something snapped, and Hisui roared.

"FIRE DRAGON'S IRON ROAR!!!" Hisui broke the ground as she blasted into Erigor's stomach with her head. She then snapped up and locked her legs around Erigor's neck. With one mighty breath, she unleashed a dragon looking fire roar, snapping every bone in his body, starting with his skull. When he fell to the ground, Hisui crawled over to Natsu. His eyes fluttered open and he smiled.

"Nice job Flame Princess."