Our Blood Oath, Volume 1: Blood Oath Brothers (Our Blood Oath #1-7)

Shin the orphan was taken in by a vampire couple who later gave birth to a younger brother for him. Life was good for a time, but when a long-haired vampire kills their parents, the younger brother, Ko, is in peril. Desperate, Shin and Ko make a Blood Oath of Darkness. But what does this mean for them?!