Blood Control allows the user to manipulate their own blood after it has left their body.
Once the blood is out in the open air, the user can freely control its flow and movements, as well as harden it to immobilize foes.
Blood Control also appears to allow the user to go unaffected by levels of blood loss that would normally be fatal.
Vlad King uses special gloves, which are connected to tubes attached to various parts of his body, to release large amounts of blood quickly. He can also reabsorb his blood back through his gloves.
- My Hero Academia Manga: Chapter 82.
- Blood - Wikipedia article about the substance Sekijiro can manipulate.