Long before the events of Don't Call Me Dirty, Hanao Kaji and Ryuuji Mita were close friends...
When Ryuuji is left to raise his son Shouji as a single father, Hanao steps up to help him out. At first, their family life is happy and content, but Hanao's true feelings for Ryuuji become more and more difficult for him to ignore. The pressure of staying closeted eventually becomes too much to bear; Hanao leaves, choosing to run from his feelings and his fears of somehow "messing up" Shouji's life when he starts getting teased at school for having two dads. 

Years later, when he comes home to care for his aging father and ends up advising Shouji on his blossoming relationship with Hama, Hanao realizes it's time to face his own past... and his future.