Shounen wa Ouji

On his way home from track practice just before an important competition, Yukiya from the track and field club witnesses a bag-snatching incident. He uses his impressive speed to catch the thief, but just as he does, he’s suddenly engulfed in a mysterious light and transported to another world. The one who summoned him is a boy named Daryu, who appears to be under a curse.

"Form a contract with me." While Yukiya struggles to make sense of the situation, Daryu demands his blood to break the curse and return to his original form. Just then, they are attacked by vicious beasts and suspicious men in black. Soon, Yukiya learns that the boy whose life is being targeted is actually Darius, the second prince of the kingdom. What will Yukiya do next?

(Source: Kadokawa, translated)

Note: Includes two extra chapters.