Fate x Baki
Shirou never really remember of his father, ever since he came out of that flame he can somewhat vividly remember his mother face but not his father's.
This is why for him Kiritsugu is always his real dad, but then one day not long after Kiritsugu's death a giant man that looks like an Ogre came and claim to be his father. Out of nowhere, he forcefully take him away from his home, and ever since then he forcefully make him to have spar with him.
However, never have Shirou managed to even land a blow on this man, not even when he is asleep.
"...Pathetic, to think you who inherit my gene is this weak. Yet, you speak big about becoming Hero of Justice."
"I don't want to be a hero of Justice, I will be one!"
A story of Shirou being Hanma Yujiro's son, and how the two interact