Ragna

Ragna (ラグナ, Raguna) is a dragon hunter who teamed up with Crimson, so they could kill all dragons.

Plot
Ragna spent his time with Leonica killing dragons, but due to being weaker than her, he trained his swordsmanship after she went to sleep. He started having visions of losing everything. One day they heard news of the nearby village being attacked by dragons and moments later their town was attacked by dragons who were led by a superior dragon. Ragna tried attacking him, but was easily defeated and thrown into the river.

As Ragna was sinking into the river, his future self appeared, telling him that he is now strong to face even the dragon king, but he had lost everything he wanted to protect. The present Ragna then begs for his future self's power, so that he could protect Leo. His future self then gave him his power. Ragna then with his newly obtained power started to decimate the dragons with ease and went to face the superior dragon. Fearing Ragna he unleashed his true self and power, but was easily defeated by Ragna.

Power & Abilities
Original timeline

Silver Blood Arts

Ragna possessed no talent for dragon hunting. But due to his countless battles against dragons, his silver sword fused with his body allowing him to develop a unique form of martial arts, Silver Blood Arts. He is able to produce silver aura, a specific kind of energy that can freeze the magic that runs through a dragons blood. The nature of this ability allows him to challenge and put down even the strongest dragons. He can imbue weapons with silver aura making them far more effective at killing dragons, summon silver swords to use as projectiles or in melee combat. He can also manipulate silver aura outside of his body, allowing him to use it as a projectile. Using this and Crimson's help Ragna managed to slay every high ranking dragon other than the Dragon God itself.

Physical capabilities

While initially being too weak to handle even base line dragons, through years of battle, Ragna became one of the strongest dragon hunters to ever exist. His speed and power were further augmented to unknown levels with the use of Silver Blood Arts. The extent of this Ragna's strength and speed have not been shown, but given how he was able to slay all of the upper class dragons and their king, it can be assumed that his strength and speed surpass any human or dragon.