Hellsing follows the antiheroic vampire, Alucard, and a police girl-turned-vampire, Seras Victoria, two vampires employed by the vampire-extermination group of England, the Hellsing Organization. Slowly but surely, through their active duty, they find a new breed of vampires beginning to arise.

Decades ago, the legendary Dr. Abraham Van Helsing and his companions defeated Count Dracula, one of the world's deadliest vampires. After this success his name was used in the founding of the Hellsing Organization, a British task force with the duty of eliminating supernatural threats. Hellsing follows the exploits of that very organization. Led by Integra Fairbrook Wingates Hellsing, the Hellsing Organization finds its trump card not in the power of man, but in the strength of a monster it has tamed. Alucard, one of the oldest and most powerful vampires in existence, now hunts his fellow monsters at Hellsing's bequest. Alongside new recruit Seras Victoria, Alucard will find that a new threat has arisen, one greater than anything the Hellsing Organization has ever dealt with before.

Vampires exist. It is the duty of Hellsing, a secret organization sponsored by the British government, to hide that frightening fact and protect the blissfully unaware populace. Along with its own personal army, Hellsing has secret weapons. Alucard, an incredibly powerful vampire, has been controlled by Hellsing for years. It is unclear how he feels about being a servant to the Hellsing family, but he certainly enjoys his job as a vampire exterminator. Seras is a fledgling vampire and former police woman. Although reluctant to embrace her new self, she is a valued member of the organization. Integra Hellsing, the current leader, is usually fully capable of fulfilling her duty, but lately, vampire activity has been on the rise. Unfortunately, the cause is more alarming than anything she could have imagined. A group long thought dead has been plotting in secret since their apparent destruction over 50 years ago.

There exist creatures of darkness and evil that plague the night, devouring any human unfortunate enough to be caught in their grasp. On the other side is Hellsing, an organization dedicated to destroying these supernatural forces that threaten the very existence of humanity. At its head is Integra Fairbrook Wingates Hellsing, who commands a powerful military and spends her life fighting the undead. Integra's vast army, however, pales in comparison with her ultimate weapon: the vampire Alucard, who works against his own kind as an exterminator for Hellsing. With his new vampire servant, Seras Victoria, at his side, Alucard must battle not only monsters, but all those who stand to oppose Hellsing, be they in the guise of good or evil. In a battle for mankind's survival, Hellsing Ultimate proves that appearances are not all they may seem, and sometimes the greatest weapon can come in the form of one's worst nightmare.