He Ascended... - S1.E15

Rin's master shows up, trying to make her go back to the head family since Kazuki is dead. Rin pretends to be betrothed with Kazuki, and Rin's master wants to fight Rin and Kazuki as to show he is good enough to marry Rin. Rin's master later told Kazuki a bit about Rin's past and how he was forced to become cruel to Rin instead of the kind "big brother" when he was named her master. He also told Kazuki that what Rin needs now isn't intense training, but someone to allow her to feel the warmth of friendship, which he deprived Rin of when she was a child. A week later, the duel took place, which went short when Rin's master collapsed due to old age. As his time nears, he apologized for all the harshness he done to Rin as her master, hoped for her forgiveness and bade Rin farewell; then he died, his soul went to the moon and Rin cried over his body.