Ninjas and Devils

2 boys. Found and raised together. Though not connected by blood, they are the closest thing they have to the family for each other. They were trained by a faction called the 'Arishikage' Apparently, they are a faction that is hidden from the original 3. Devils. Angels. And Fallen Angels.
But as time went by, 1 brother wanted to prove that he was stronger and left the clan and dived into the interdimensional war between the 3 factions. The lone brother has sworn to defeat his brother and not rest until he has. And then... He can find peace.