Cecily Campbell is the head of the Campbell house and a member of the 'Knight Guards' responsible for protecting the Independent Trade City of Housman. When Cecily's sword is broken in a confrontation with a former knight she must search for a blacksmith to repair it. Unfortunately the only person skilled enough is Luke Ainsworth, who also happens to be the one who saved her life during the earlier fight. However, before he can even start his task Luke must once again save Cecily's life when a local trade caravan is attacked by monsters.

Luke is able to use his newly forged katana to defeat the demons attacking the trade caravan and protect Cecily. Following this Luke reluctantly agrees to make Cecily a new sword, but she quickly finds that the price may be prohibitive. Cecily is then given a new assignment to protect a very special girl named Aria.

Cecily is assigned to protect the Demon Sword, Aria whilst in her human form and asks Lisa to join her as she shows her new charge around the City. However, their peaceful day out is cut short when the mysterious man in black uses possessed prisoners to attack the town. But can the kind hearted Cecily really kill a human opponent?

Despite her misgivings Cecily is ordered to use Aria to lure out the mysterious man in black. However, when things go wrong and the situation gets out of hand Cecily must once again ask Luke for help so that she can protect her new friend.

After spending more time with Luke and Lisa Cecily begins to wonder about their relationship and tells Luke he should be more considerate towards Lisa. This leads to the girls taking Lisa shopping, and Luke agreeing to pay!

Cecily and Aria are attacked by a young woman called Doris who is bodyguard to Princess Charlotte Firobisher. Although it seems like Cecily has the upper hand things change when it emerges that Doris commands the Demon Sword of Earth, Claymore. Doris is also not alone she is accompanied by Margot, who commands the Demon Sword of Scarlet Ray, Rhomphair and Penelope who wields the Demon Sword that Slays Demon Swords, Ballock Knife. Meanwhile, Princess Charlotte herself confronts Luke using the Demon Sword of Black Flames, Evadne. However, it soon becomes clear that these four women are not the murderous thieves they first appear to be.

Charlotte and the others are forced to work as maids in exchange for staying in the Campbell house and unfortunately for her Cecily gets roped in as well. However, whilst living and working together Cecily begins to learn more about her new friends and Charlotte in particular. Meanwhile Aria talks to Evadne about what it means to be a Demon Sword.

When the Empire refuses to accept Charlotte's status she is forced to defect to the Militant Nation in order to protect the City of Housman from the Emperor's wrath. However, Doris and the other's believe they may be able to buy the Empires acceptance by handing over the Demon Swords and Luke! It then falls to Cecily to talk some sense into them before it is too late.

Luke is off to visit the grave of an old friend, Lisa Oakwood as he does every year and for the first time he asks someone to join him, Cecily. While Luke and Cecily are off paying their respects Lisa is left to repair a precious dagger belonging to a young girl named, Elsa. Unfortunately, Elsa is not all that she appears to be.

Following the attack on Luke and Lisa, Cecily wants to know why Luke is being targeted. She soon learns that Luke may be the only of blacksmith with the skill to create a 'Sacred Sword' capable of slaying the God, Valbanill. Not only would this end Valbanill's curse and save the world but also exact the revenge that Luke craves. However, Siegfried is determined to stop him by any means necessary.

Following the revelation that Lisa is a demon, Cecily begins to avoid both her and Luke. However, she soon realises how foolishly she has been acting when she is invited to attend a conference concerning Valbanil and the Sacred Sword, which Luke and Siegfried also attend. Unfortunately, the revelations at the conference only serve to fuel Siegfried's anger and he decides it is time to put his plans into motion.

After his humiliation during the conference Siegfried finally snaps and dispatches a horde of demons to destroy the City of Housman. While Cecily and Aria join the Knight Guards in dealing with the demons, Luke decides it is time to settle things with Siegfried. However, even Luke may not be strong enough to stand against Siegfried's Demon Sword of Darkness, at least not without help.