Ragna the Bloodedge

Ragna the Bloodedge (a.k.a. "The Grim Reaper") has one hell of a troubled past. Apparently, his brother Jin (or Terumi) cut off his arm, kidnapped his sister Saya and burned down his orphanage when he was a kid, leaving him for dead. For some reason, Rachel decided to resurrect him as a (half-)vampire, causing one of his eyes to turn red.
 
After somehow getting a replacement arm containing the Azure Grimoire, Ragna decided to go around the world and destroy the bastions of the Novus Ordus Librarium (a.k.a. "The Library" or the "NOL") for reasons known only to him. Of course, his actions have caused the Library to label Ragna an "SS-class threat" and place the largest bounty in their history on his head, which in turn caused everyone from Library soldiers to random vigilantes to hunt him down. Though many seek the bounty, some also want to possess his Grimoire and the incredible magic power it is rumored to hold. 

Calamity Trigger

As the story progresses, Ragna blames Jin for the loss of his arm and near death experience as a child, though apparently the evil being Terumi was behind it all along in an attempt to manipulate the time loop for his own goals. However, it's also hinted that Jin and Ragna are actually brothers by blood, and not just by name. Later, V-13 appears before him near the Cauldron hidden deep within the main library of Kagutsuchi, and gains a yandere streak in his presence, but Ragna gets even more pissed off because this time v-13 is using a face and voice similar to that of his dead sister Saya. 
 
V-13 wants to merge with Ragna at all costs in order to form the evil Black Beast, and it's revealed that Ragna had to fight V-13 at least two times before as he went to destroy previous libraries. In many story arcs, whether the character wins or loses, V-13 simply stabs a wounded Ragna through the torso and drags him with her into the Cauldron, forming the Black Beast and repeating the time loop over again. Ragna forms the body of the Black Beast, while v-13 forms the heart. As the Black Beast, Ragna is fully aware of his actions, but can do nothing to stop them. 
 
In the "True Ending," Ragna is about to be absorbed with V-13 along with his fragment of the Azure Grimoire, but Noel saves him at the last minute, dredging up a flashback of Saya. Also, Rachel appears and mentions that Ragna is not carrying the real grimoire, but a mere fragment of it. The true grimoire ends up in Noel's possession, though she inadvertently shares it with Terumi by the story's end.
 

Continuum Shift

Ragna manages to drag himself away from the Library after the injuries he sustained fighting with Jin, Hakumen, v-13 and Hazama consecutively from the last game. Noel tags along behind him, wanting to know more about why she saved him, but Ragna angrily tells her to piss off. Noel goes to leave, but then promises she will fight him as an enemy the next time they meet. However, before Ragna can rest, he is attacked by Carl and Nirvana and lapses into unconsciousness.
 
Through a series of flashbacks, Ragna reveals more about his childhood: that the Azure Grimoire somehow became a replacement for his right arm after it was cut off, and that Jubei trained him heavily with Rachel's encouragement. "The Bloodedge" moniker apparently came from an old war buddy of Jubei's who wore the same coat and carried the same sword that Jubei later gave to Ragna, saying that friend bought the Six Heroes enough time to come up with a plan to kill the Black Beast during the Dark War.
 
Ragna later wakes up in the care of the Kaka clan, trying to search for the one person most responsible for destroying his life: Terumi. After fighting against Jin once again, he manages to reach Terumi in his guise as Hazama and fights him as well. He activates his fragment of the Azure Grimoire (or the "BlazBlue", as the dubbing got a little mixed up here) in order to curbstomp Hazama, but to his surprise, Hazama gives the same incantation he used and fights Ragna with his Unlimited form as well in the game. When Ragna has trouble understanding, Hazama reveals that he (Terumi) was the one who originally created the Azure Grimoire. While Ragna's BlazBlue is a mere fragment, he has the real thing. 
 
Hazama strangely stops in the middle of battle, and then shows Ragna that the whole point of fighting him was to buy time so that Noel could finish her transformation into Mu-12. On top of that, Hazama shares a "lifelink" with Mu-12, meaning that the only way to kill him permanently would be to kill Mu-12 and Hazama at the same time. After ordering Mu-12 to enter the Cauldron from the last game and destroy Murakumo, Hazama then decides to finish off Ragna as Ragna's own power cannot beat Hazama. Just as he tries to land the killing blow with his Ouroboros, Lambda-11 shows up and throws her body in front of the chain, sacrificing herself in the process. It turns out that Nu-13's soul awakened within the 11th unit and her love for Ragna led her to sacrifice Lambda's body so Ragna could gain her fragment of the Azure Grimoire as well.
 
With his BlazBlue recharged, Ragna manages to beat down Hazama and runs back down to the Cauldron buried deep in the Library from the last game. After pulling Rachel out of a magic trap, he begins to fight against Mu-12 in an attempt to bring Noel's personality back. He sacrifices his own left arm to destroy the armor surrounding Mu-12's head, successfully bringing Noel back but not without wounding himself in the process.
 
While the heroes are slowly trying to take stock of the situation, Hazama reappears and threatens to kill them all, but he is stopped when the Imperator Librarius herself decides to appear in person in front of them. Upon seeing her face, Ragna immediately knows her true identity as his sister, Saya, who was supposedly kidnapped by Hazama several years ago.
 
Eventually, Ragna is given a new regenerated arm from Lambda's biotank thanks to Kokonoe, and he decides to head to the ruined city of Ikaruga to find whatever he can to stop the Imperator and her subordinates. Taokaka ends up tagging along behind him.
 

Gameplay

(as of Continuum Shift)
Pros:

• Easy to pick up and learn with simple combos
  
• Close range attacker, but his specials can close the distance very fast.
• Drive can drain a little HP and restore your own, even if blocked.

Cons:

• Has lower maximum HP than half the playable cast
• Specials come with a slightly long recovery time.
• No real long-range attacks.
  

 
Basic Special Moves:

• Hell's Fang (214A) and Tsuika (214D, performed right after Hell's Fang): Ragna charges with a straight horizontal punch across the ground and follows up with a second standing punch through Tsuika. Useful for closing the distance with your opponent or for finishing a combo.
  

   ( NOTE: 5B, 5C, 214A -> 214D is the most basic combo Ragna has, and it will wipe out 1942 HP from your opponent if it all connects. Learn it.)

• Gauntlet Hades (214B) and Keri Age (214D, performed right after Gauntlet Hades): Gauntlet Hades is similar to Hell's Fang, except Ragna punches in an overhead arc with his glowing hand, then does a spinny kick with Keri Age. This one does slightly more damage than Hell's Fang and can be performed in midair, but if it's blocked Ragna is in a lot more danger.
• Inferno Divider (623C/D): Basic anti-air special (think: SHORYUKEN! with a sword). Useful for countering rushing and jumping characters, but very unsafe on block. Pushing C will attack normally, pushing D will add Ragna's Soul Eater Drive property and steal a little health as well.
  

  ( NOTE: If it hits, can be chained into the following special moves...)

• Upper (236C after Inferno Divider): Ragna follows with an uppercut
• Yoko Fukitobashi (236C after Upper): Ragna follows his uppercut with a straight punch that can bounce the enemy off a wall, allowing you to set up another combo shortly after if you're quick.

OR

• Kakato Otoshi (214D after Upper): Ragna slams the opponent down to the ground and can drain a small amount of HP (100-250?) from him/her.
• It's Not Over Yet! (22C on downed enemy): Ragna picks up the enemy and punches them in the gut. If your opponent hasn't tech-rolled off the ground yet, use this to continue pressuring him/her.
• Belial Edge (214C in midair): Ragna spins towards the enemy at a downwards angle. Useful for finishing air combos.

 
Distortion Drives:

• Carnage Scissors (632146D): Ragna dashes across the screen, smacks the enemy with his sword, then releases a large amount of dark energy with a second hit that can drain anywhere from 300-1000 HP depending on whether or not this was part of a combo. Useful if you want to catch someone who is throwing a projectile at you, but only has a few invincibility frames, so beware.
• Blood Kain (214214D): Ragna's body emits a black aura for 10 seconds. The good news is that all attacks are faster, more powerful, and the Soul Eater will drain more health during this time. The bad news is that Ragna's own health is constantly being drained by this power, up to 3000 HP. So use this time wisely.
• Devoured In Darkness (214214D, during Blood Kain): A close-range attack where Ragna grabs the opponent and drains a ton of their health for himself. Automatically ends Blood Kain when used. However, you still need 50% Meter after Blood Kain's use to use Devoured In Darkness. Also, Ragna can be poked out of this DD right at the start of his animation, so watch out.

 
Astral Heat:

• Black Onslaught (2141236C): Ragna strikes the opponent with his sword, turns it into a scythe, then slices through the enemy several times before turning them into nothing with a final cut. Invincible on start-up.