Corrected entry: Kira has Oishi, his worst enemy, trapped in a dungeon under heavy guard for an entire year, but suddenly decides to release him and send him off without even keeping a watch on him. And conveniently, this all happens just in time for Oishi to stage his revenge and prevent Kira's marriage to Mika.
Corrected entry: In the scene where Oishi and Kai escaped the slave fighting pit and they are both walking alongside their horses, talking to each other, they stand still and Oichi gives clothes to Kai. Afterwards, Oishi gets on his horse from the horses' right side, while having his sword strapped in his belt. The whole reason we (the people of today) still get off and on horses from the left is exactly because of swords. Swords were carried on the left, which meant you'd have to get on your horse from the left for the sword not to be in your way. Oishi does the complete opposite to stay in the shot with Kai. A little later Kai gets off his horse from the right side to stay in the shot with Oishi. (00:49:40)
Correction: He told his soldiers to break his hope. And He told him "you'll be released when I'll be married to the girl". But then, he has other plans than let Kira take his village. That's why he kept him alive. Just to let him watch this and be desperate.