The mauling of a vicious, prehistoric-sized African elephant makes international headlines. Featured in reports of the aftermath, the sole survivor of one of the animal's rampages attributes its death to a lone, unarmed man—unknowingly describing Yuujirou Hanma, nicknamed the Ogre and often labeled as the strongest creature on Earth. Elsewhere, Yuujirou's 18-year-old son Baki spars with an equally formidable beast: a praying mantis. Content with his training and determined to overtake his father, Baki abducts American President George Bosch to begin his plans. This leads to his deliberate imprisonment at the infamous Arizona State Prison where Oliva Biscuit resides—the strongest man in the United States and an inmate allowed to leave of his own volition. Hoping to gauge his abilities, Baki challenges Oliva to a fight; but Oliva is preoccupied with his eccentric rival, Jun Guevaru. Known as the Second, he is the only other prisoner to receive special treatment from the guards. Bewildered yet intrigued, Baki learns about his fellow inmates and tolerates the hellish conditions of prison life while waiting for an opportunity to present itself.

Satou Matsuzaka is a beautiful high schooler who has a reputation for being permissive with men. However, a chance encounter with a young girl named Shio Koube makes Satou realize that this is her first and only true feeling of love. Telling others that she lives with her aunt, Satou secretly shares an apartment with Shio. Despite her innocent appearance, Satou is willing to do anything to protect her beloved, resorting to desperate measures to ensure that their happy sugar life remains intact.

During the height of World War II, Nazi Germany seeks to strengthen their soldiers with technology crafted under the influence of vampiric biology. Out of fear of this technology turning the tide of war in the Axis's favor, Sir Arthur Hellsing enlists his butler and soldier Walter C. Dornez and vampire Alucard to put a stop to the German plot, sending the two men into a conflict that will scar them both forever.

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.