Here's the rewrite, keeping your opening and the sparring section up to the rib kick, then continuing in your voice:
---
A month had passed since the death of Ivan.
After the duel, Dravania couldn't be more proud of their golden boy.
They threw many festivals in his name and invited him to many events.
However, Derrick declined them all and remained in his manor.
He had claimed his prize, thirty percent of Ivan's estate, wealth and weapon stores.
Despite all this, Derrick really wasn't happy. How could he be when he hadn't seen his father?
The king had vanished without a word, not even a personal congratulations.
Derrick spent his days by Royal Knight's side, just watching him breathe while the Varyn infection slowly spread.
He knew staying beside Royal Knight all day wasn't the best for him, which was why he decided to continue his training with Sir Thompson.
In the sparring grounds of Sir Thompson's estate, both men were currently engaged in combat.
