I was a Slave to Two Assassins and I loved it

A dangerous discovery by accident causes 17-year-old Asuka Caballeros, a half-Japanese, half-Filipino high school boy of Spanish descent, to be sucked into the world of assassins and action.
3 years after the tragic death of their parents, he and his younger sister, Niko, were forced into a blood pact with two well-known and highly-skilled assassins, Akihito and Aki Hirona, children of a rich family, when one of them found a USB containing very confidential information.
Now slaves to the two assassins, Asuka and Niko will both soon discovered their father’s secret past, and their relationship with Akihito and Aki as slave and master will quickly blossomed into a circle of friendship, with two of them slowly falling in love with one another.
But, how their relationship would blossom more than just mere slave and master?