Blood Knights is a medieval vampire hack 'n' slash game where vampiric skills are combined with blade fighting. There are two playable characters: the sword-wielding and melee-focused vampire-turned vampire hunter Jeremy, and Aylsa, a vampire Jeremy became ritually bound too, using ranged attacks with her crossbows. The game is set on a fictional version of Earth where vampires and humans are at war. Originally enemies, Jeremy is cast out after having become a vampire and needs to work together with Alysa to pursue the vampires who stole the Blood Seal, a powerful artifact.
Players need to slay hordes of monsters, either in single-player or in local co-op. In single-player it is possible to alternate between the two characters at any time and both are always present, with one controlled by the AI, while in co-op both are controlled by a player simultaneously. By exploring levels and defeating enemies new weapons (about 160) and armor types (about 40) can be found. Both characters have different attacks that can be combined into combos and there are boss battles. Powerful special attacks have a cooldown time. Unlike Jeremy, Alyssa is controlled as in a twin stick shooter with one set for movement and another for aiming the ranged attacks. Sucking blood is used to replenish health and it is possible to transfer blood from one character to the other, providing health at the expense of the giver. It is also possible to interact with the environment using attract and repel skills.