There are key differences in the sword design through the movie and series. In the original anime movie the sword is simply a sword - all that is needed to kill the chiropteran is massive bloodloss. In the television series however the sword has a distinct groove running through the center and to the edges, allowing Saya's blood to run through it.
Just like in the television series, in the 45-minute OVA Saya owns not one but two swords. Following the death of her first victim on the subway Saya complains to her handler David that the sword is getting dull and she wants a new one - even though, as David says, "Swords of that quality are not easy to come by." Despite this she is never seen without her precious weapon, even carying it aound the school hallways in a specialised case. Saya is later seen looking at a pawn shop displaying a katana, although it is clearly marked "Not for Sale".
This original sword is damaged when Saya tries defending the nurse from two vampires (in the form of young girls) who are about to attack her. One of the vampires throws the medicine cabinet in front of her just as Saya is about to strike, resulting in the tip of the sword breaking off. Saya then rushes to the pawn shop she saw earlier and breaks into the case, stealing the sword. At this point the vampire has hidden itself among the party guests at the halloween ball when Saya once again tries attacking it. However when she strikes the monster the swords simply crumbles like tin foil - it's a fake.
Saya gains her second sword during one of the last and most dramatic scenes in the movie. Trapped under a Chiropteran intent on killing her she calls out to David, he however is unable to get inside the building. The nurse runs down the door and allowing David in - the surprised chiropteran loses it's concentration, allowing Saya to kick it off of her. At this crucial moment Saya yells "Sword!" and David throws it to her, still inside it's case, and in one swift motion, she removes the covering and slices the vampire completely in half.
The First Sword
In the TV series the sword is customized, specialy made for use of Saya's blood easily in combat. In the second half of the series, the sword was broken and replaced with a sword of diferent style but same purpose.
The first Saya's Sword has been refered as: "Khopesh" and "Sickle-Sword" because of it's shape or "One Night Kiss" by fans, but the sword itself is never named in Blood+ series. The sword is seen first in the first chapter of the series, under the custody of Hagi, who keep it in his cello's box, where it remains when it is not in use.
The shape of the sword is that of a traditional katana modified in the base of the blade in the form of a "S", similar of those of the ancient kopesh or sicke-sword. The long of the rest of the blade have and extra "Hi", started in the S shaped curve, with three more cuts beggining in this. The idea is that Saya would be able to touch the curve of the blade and cut her finger (or hand) to let her blood run in the grooves of the blade, making it a lethal weapon against chiropterans.
The true origin of this sword is not revealed. Although it may seem like a modern sword, in a chapter when Saya remembers a past life, she is seen with this sword and seem to been using it for some time. It is speculated that it was given to her from Red Shield when she first made contact with them in the past (this may explain why the Red Shield has the sword during the Vietnam Incident).
During Saya's first confrontation with Amshel Goldsmith in Russia, the sword was broken in half and left behind by her, although the blade is found by David. This part may be used as base to forge the second sword since both have a similar shape.
Saya's Second Sword
At the start of the second half of the series, Saya's broken sword is replaced by Red Shield with a new sword given to her by David , who called it "Fang", but is not revealed if it's the name of the sword (he said "This is your NEW Fang", and may refer that the first sword's name was Fang too) and is never called that again.
Saya's Second sword was a katana too with similar purpose that the first but with different shape. In this new sword, the "S" shape is relpaced by an extra metallic sharp section in the base of the blade, for Saya to cut her own hand and let her blood in the blade. This katana contained a chiropteran crystal recovered from George Miyagusku, Saya's foster father, and was supposed to give sentimental support to Saya. The rest of the blade is identical to that of the first sword, giving the clue that the Red Shield made the first sword as well.
In the final confrontation with Amshel Goldsmith, half transformed in his chavalier form, Saya gives this sword to Hagi with her blood for him to finish Amshel with. When the Metropolitan Opera House collapsed, Hagi, Amshel and the sword were buried and the fate of the sword remains a mystery.