Strange Blood

Looks like the LOU Lab is hiding something, a big secret. While this secret is kept hidden, a group of friends decides to find the reason behind the unfairness with the sweat blooded people. In this world the humans are sorted into groups of blood. Sweet blood and bitter blood. The bitter bloods are given a chance, to live. But the sweet bloods are killed because of the attraction they cause to the unknown. Something which is a secret. Something which is not just in imaginations. What is it? Are there only 2 bloods present ? Is there something missing?