Blue Secrets

(M/n) (L/n) was an ordinary boy, until he was abandoned by his deceased parents who were killed in the "Blue Knight" incident by Satan himself. He was only a child at the time, homeless and dirty as he wandered the streets wondering if his parents would come to pick him up, instead he met someone else. A man by the name of Shiro Fujimoto. He didn't hesitate to take the boy in after seeing his condition, asking about his parents whereabouts only to receive a shrug of the shoulders, so he let him stay at the monastery as an official family member. He met an outgoing blue haired twin and a shy brunette twin, the three got along pretty well as if they knew each other. What will happen when they find out about Rin's secret?