I Can't Love You
Yuuma Isogai gets abandoned at age 8, and stays at an orphanage for 7 years. He finally gets adopted by the Maehara family: a father, mother, and a boy the same age as Yuuma himself.
Yuuma knows that this family made a mistake to take him in, but they are kind and loving. Except for Hiroto, their son. Yuuma tries not to fall for him, but it's impossible. Yuuma knows that Hiroto will be weirded out, since they are 'brothers', but how will Maehara react?
Because it's not what Yuuma expects.