@teeds King Mayu (old dude in tube) was a survivor of the original cataclysm that brought forth the albinos. In an effort to fix the world he set up the system of Ryuumas, warriors equipped with the lost technology weapons of the specialist brigades from before the cataclysm. When a Ryuuma died, another would take his place and accept the weapon the previous Ryuuma used, to keep up the fight and bring hope to humanity. The ultimate goal was always to combine the powers of all the Ryuumas to attack the tower and bring it down. The Ryuumas have tried over several generations until they finally succeeded, but they all died in the process. However, the fall of the tower made things worse, so King Mayu's soldiers killed him in despair, lead by King Mizgard. In the new post-tower world, people still believe in Ryuuma and some still continued the tradition. Unfortunately, they can't succeed at anything because the end goal of the Ryuumas as planned by King Mayu was already achieved. So every time a Ryuuma fails, Mizgard either recruits him or executes him as a "false" Ryuuma because he can't really afford to get rid of the people's hope in Ryuuma.
That said, there is now for the first time in centuries a Ryuuma truly worthy of the people's hope. All the previous Ryuumas were just strong-willed human beings, but the female Ryuuma is actually a superhuman born of the tower. This is her story.